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WaMu Asset Acceptance Corp., et al. – ‘424B5’ on 7/26/06

On:  Wednesday, 7/26/06, at 2:08pm ET   ·   Accession #:  950117-6-3153   ·   File #s:  333-130795, -22

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  As Of                Filer                Filing    For·On·As Docs:Size              Issuer               Agent

 7/26/06  WaMu Asset Acceptance Corp.       424B5                  1:3.3M                                   Command F… Self-Filer/FA
          Washington Mutual Mtge Pass-Through Certificates WMAL… 2006-AR6

Document/Exhibit                   Description                      Pages   Size 

 1: 424B5       Washington Mutual Wmalt 2006-Ar6                    HTML   3.17M 

Prospectus Supplement to Prospectus Dated January 6, 2006

Washington Mutual Mortgage Pass-Through Certificates,
WMALT Series 2006-AR6

WaMu Asset Acceptance Corp.

Depositor

Washington Mutual Bank

Servicer

Washington Mutual Mortgage Securities Corp.

Sponsor

$857,591,100

(Approximate)

The underwriter listed below will offer the offered certificates at varying prices to be determined at the time of sale. The proceeds to WaMu Asset Acceptance Corp. from the sale of the offered certificates will be approximately 101.04% of the principal balance of the offered certificates plus accrued interest, before deducting expenses. The underwriter's commission will be the difference between the price it pays to WaMu Asset Acceptance Corp. for the offered certificates and the amount it receives from the sale of the offered certificates to the public.

Neither the SEC nor any state securities commission has approved or disapproved of the offered certificates or determined that this prospectus supplement or the prospectus is accurate or complete. Any representation to the contrary is a criminal offense.

Underwriter

WaMu Capital Corp.

July 25, 2006

Important Notice About Information Presented in this
Prospectus Supplement and the Accompanying Prospectus

      We provide information to you about the offered certificates in two separate documents that progressively provide more detail: (a) the accompanying prospectus, which provides general information, some of which may not apply to your series of certificates, and (b) this prospectus supplement, which describes the specific terms of your series of certificates.

      You should be certain to review the information in this prospectus supplement for a description of the specific terms of your certificates.

      We include cross-references in this prospectus supplement and the accompanying prospectus to captions in these materials where you can find further related discussions. The following table of contents and the table of contents included in the accompanying prospectus provide the pages on which these captions are located.

      You can find a listing of the pages where some of the capitalized terms used in this prospectus supplement and the accompanying prospectus are defined under the caption “Index of Terms” on page S-135 in this prospectus supplement and under the caption “Glossary” beginning on page 142 in the accompanying prospectus. Capitalized terms used in this prospectus supplement and not otherwise defined in this prospectus supplement have the meanings assigned in the accompanying prospectus.

European Economic Area

      In relation to each Member State of the European Economic Area which has implemented the Prospectus Directive (each, a “Relevant Member State”), the underwriter has represented and agreed that with effect from and including the date on which the Prospectus Directive is implemented in that Relevant Member State (the “Relevant Implementation Date”) it has not made and will not make an offer of certificates to the public in that Relevant Member State prior to the publication of a prospectus in relation to the certificates which has been approved by the competent authority in that Relevant Member State or, where appropriate, approved in another Relevant Member State and notified to the competent authority in that Relevant Member State, all in accordance with the Prospectus Directive, except that it may, with effect from and including the Relevant Implementation Date, make an offer of certificates to the public in that Relevant Member State at any time:

      For the purposes of this provision, the expression an “offer of certificates to the public” in relation to any certificates in any Relevant Member State means the communication in any form and by any means of sufficient information on the terms of the offer and the certificates to be offered so as to enable an investor to decide to purchase or subscribe to the certificates, as the same may be varied in that Member State by any measure implementing the Prospectus Directive in that Member State and the expression “Prospectus Directive” means Directive 2003/71/EC and includes any relevant implementing measure in each Relevant Member State.

United Kingdom

      The underwriter has represented and agreed that:

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TABLE OF CONTENTS

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SUMMARY INFORMATION

The following summary highlights selected information from this prospectus supplement. It does not contain all of the information that you need to consider in making your investment decision. To understand the terms of the offered certificates, read carefully this entire prospectus supplement and the accompanying prospectus.

This summary provides an overview of certain calculations, cash flows and other information to aid your understanding. This summary is qualified by the full description of these calculations, cash flows and other information in this prospectus supplement and the accompanying prospectus.

TRANSACTION PARTICIPANTS

On July 27, 2006, which is the closing date, the mortgage loans that support the certificates will be sold by Washington Mutual Mortgage Securities Corp., the sponsor of the securitization transaction, to WaMu Asset Acceptance Corp., the depositor. On the closing date, the depositor will sell the mortgage loans and related assets to the Washington Mutual Mortgage Pass-Through Certificates WMALT Series 2006-AR6 Trust. In exchange for the mortgage loans and related assets, the Trust will issue the certificates pursuant to the order of the depositor.

The sponsor purchased the mortgage loans directly or indirectly from affiliated or unaffiliated third parties who either originated the mortgage loans or purchased the mortgage loans through correspondent or broker lending. Approximately 23.6%, 13.2%, 11.0% and 11.0% of the mortgage loans (by principal balance as of the Cut-Off Date (as defined in “Description of the Mortgage Pool” in this prospectus supplement)) were originated by Alliance Bancorp, First Horizon Home Loan Corporation, Plaza Home Mortgage, Inc. and Residential Funding Corporation, respectively.

The mortgage loans will be serviced by Washington Mutual Bank, as servicer. Some servicing functions will be performed by Washington Mutual Mortgage Securities Corp., as administrative agent of Washington Mutual Bank. Some servicing functions will be outsourced to third party vendors. Some mortgage loans will be serviced by either the respective originators of those mortgage loans or the entity that sold those mortgage loans to the sponsor on an interim basis until the servicing is transferred to Washington Mutual Bank. By September 1, 2006, the servicing of those mortgage loans is expected to have been transferred to Washington Mutual Bank.

The trustee of the Trust will be LaSalle Bank National Association, and the Delaware trustee will be Christiana Bank & Trust Company.

WHAT YOU OWN

Your certificates represent interests only in the assets of the issuing entity. All payments to you will come only from the amounts received in connection with those assets.

The Trust owns a pool of mortgage loans and other assets, as described under “The Trust” in this prospectus supplement.

There are no outstanding series or classes of securities that are backed by the assets of the issuing entity or otherwise have claims on the assets of the issuing entity, other than the certificates. The depositor does not expect that any securities representing additional interests in or claims on the assets of the issuing entity will be issued in the future.

Information About the Mortgage Pool

The mortgage pool consists of 2,061 mortgage loans with an aggregate principal balance as of the Cut-Off Date (as defined in “Description of the Mortgage Pool” in this prospectus supplement) of approximately $875,099,554. All of the mortgage loans are secured by residential properties (or shares of cooperative apartments) and each has an original term to maturity of not more than 40 years.

After an initial fixed-rate period of one or three months, the interest rate on each mortgage loan will adjust monthly to equal the sum of an index and a margin. As of the Cut-Off Date, approximately 21.4% of the mortgage loans (by aggregate principal balance) were still in their initial fixed-rate period. The interest rates on the mortgage loans are subject to overall maximum and minimum interest rate limits.

The index for approximately 81.9% and 98.9% of the mortgage loans (by aggregate principal balance as of the Cut-Off Date) in loan group 1 and loan group 2, respectively, will be One-Year MTA, the 12-month moving average yield on United States Treasury Securities adjusted to a constant maturity of one year. The index for approximately 18.1%

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and 1.1% of the mortgage loans (by aggregate principal balance as of the Cut-Off Date) in loan group 1 and loan group 2, respectively, will be the average of interbank offered rates for one-month U.S. dollar-denominated deposits in the London market as described in this prospectus supplement under the heading “Description of the Mortgage Loans—The Indexes”.

While the interest rate on each mortgage loan will adjust monthly (after the initial fixed-rate period), the minimum monthly payment on each mortgage loan generally will adjust only annually (except that for approximately 0.4%, by aggregate principal balance as of the Cut-Off Date, of the mortgage loans, the minimum monthly payment will initially adjust sixty months after origination of such mortgage loans, and then adjust annually thereafter). On each annual payment adjustment date, the minimum monthly payment generally will not increase or decrease by more than 7.5%. As a result, the interest due with respect to a mortgage loan for any given month may, under certain circumstances, exceed the monthly payment for that month. In that case, payment of the excess of interest due over the monthly payment will be deferred and that excess will be added to the principal balance of that mortgage loan in the form of “negative amortization.” See “Description of the Mortgage Pool” in this prospectus supplement.

In the event of a material breach of the representations and warranties made by the sponsor or the depositor with respect to the mortgage loans, or in the event that a required loan document is not included in the mortgage files for the mortgage loans, the breaching party will, unless it has cured the breach in all material respects, be required to repurchase the affected mortgage loan or substitute a new mortgage loan for the affected mortgage loan. See “Description of the Mortgage Pool—Representations and Warranties Regarding the Mortgage Loans” in this prospectus supplement.

For a further description of the mortgage loans, see “Description of the Mortgage Pool” and Appendix B in this prospectus supplement.

The mortgage pool consists of the following two loan groups:

The mortgage loans in loan group 1 are mortgage loans that do not impose prepayment penalties. The mortgage loans in loan group 2 are mortgage loans that impose a prepayment penalty for voluntary prepayments in full for a period no greater than thirty-six months from the date of origination of such mortgage loan.

THE CERTIFICATES

The Offered Certificates

The approximate initial class principal balance, annual certificate interest rate and type of each class of the offered certificates will be as follows:

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The Non-Offered Certificates

In addition to the offered certificates, the Trust will also issue the Class B-12, Class B-13 and Class B-14 Certificates. These certificates are not being offered by this prospectus supplement.

The approximate initial class principal balance, annual certificate interest rate and type of each of the Class B-12, Class B-13 and Class B-14 Certificates will be as follows:

The Class B-12, Class B-13 and Class B-14 Certificates will be subordinate in right of payment to the offered certificates and will not receive distributions of interest or principal on any distribution date until the offered certificates have received all distributions of interest and principal that they are entitled to receive on that distribution date. In addition, losses realized on the mortgage loans will be allocated to the Class B-12, Class B-13 and Class B-14 Certificates, until their principal balances have been reduced to zero, before they are allocated to the offered certificates. See “Description of the Certificates—Subordination and Allocation of Losses” in this prospectus supplement.

Relationship Between Loan Groups and the Offered Certificates

The certificates whose class designation begins with “1” or “R” correspond to loan group 1. The certificates whose class designation begins with “2” correspond to loan group 2. The certificates whose class designation begins with “C” or “B” correspond to loan groups 1 and 2. Each of the certificates generally receives distributions based on principal and interest collected from mortgage loans in its corresponding loan group or loan groups.

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Initial Principal Balance of the Certificates

The initial aggregate principal balance of the certificates issued by the Trust is approximately $875,099,554, subject to an upward or downward variance of no more than 5%.

The initial aggregate principal balance of the certificates has the following composition:

Last Scheduled Distribution Date

The last scheduled distribution date for each class of certificates is the distribution date in the month after the scheduled maturity date for the latest maturing mortgage loan in the related loan group or loan groups.

The actual rate of principal payments on the certificates will depend on the rate of principal payments (including principal prepayments) on the related mortgage loans. No assurance can be given as to the actual payment experience on the mortgage loans.

See “Description of the Certificates—Last Scheduled Distribution Date” in this prospectus supplement.

DISTRIBUTIONS ON THE CERTIFICATES

Monthly Distributions

Each month, the trustee, LaSalle Bank National Association, will make distributions of interest and/or principal to the holders of the certificates. Distributions will be made on the 25th day of each month, or if the 25th day is not a business day, on the next business day. The first distribution date will be August 25, 2006.

Source of Payments. The mortgagors pay their interest and principal during the month to the servicer. Each month, the servicer subtracts its servicing fee and sends the remainder to the trustee. On the distribution date for that month, the trustee distributes that remaining amount by loan group to the holders of the certificates related to that loan group in the order described in “Description of the Certificates—Priority of Distributions” in this prospectus supplement (in accordance with the monthly distribution report). The servicing fee will be calculated as a per annum percentage for each mortgage loan. The servicing fee for each mortgage loan (a) (1) indexed to One-Year MTA and in loan group 1, will equal (x) the greater of (i) 0.375% and (ii) the excess, if any, of the gross margin on the applicable mortgage loan (as stated in the related mortgage note) over 2.05% or (y) the initial fixed rate on such mortgage loan and (2) indexed to One-Year MTA and in loan group 2, will equal (x) the greater of (i) 0.375% and (ii) the excess, if any, of the gross margin on the applicable mortgage loan (as stated in the related mortgage note) over 1.50% or (y) the initial fixed rate on such mortgage loan and (b) indexed to One-Month LIBOR, as described in this prospectus supplement under the heading “Description of the Mortgage Loans—The Indexes”, will equal (1) the greater of (i) 0.375% and (ii) the excess, if any, of the gross margin on the applicable mortgage loan (as stated in the related mortgage note) over 1.00% or (2) the initial fixed rate on such mortgage loan.

Advances. For any month, if the servicer receives a payment on a mortgage loan that is less than the minimum monthly payment due or if no payment is received at all, the servicer will advance its own funds or funds collected by the servicer on the mortgage loans but not required to be distributed to the certificateholders on the current distribution date, to cover the difference between the minimum monthly payment due and the amount actually received by the servicer. However, the servicer will not be required to make advances if it determines that those advances will not be recoverable from future payments or collections on that mortgage loan. See “The Servicers—The Servicer—Servicing Procedures—Advances” in this prospectus supplement.

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Distributions of Interest

Each class of offered certificates will accrue interest on its class principal balance. On each distribution date interest will be distributed to these classes in the order described in “Description of the Certificates—Priority of Distributions” in this prospectus supplement.

Solely for purposes of calculating distributions of principal and interest and the allocation of losses realized on the mortgage loans, each of the Class 1X and Class 2X-PPP Certificates will be deemed to be comprised of an interest-only component and a principal-only component. Interest, if any, will be payable with respect to each Class 1X and Class 2X-PPP interest-only component. The Class 1X and Class 2X-PPP interest-only components will not have a principal balance and principal will not be payable with respect to the interest-only components. Each of the Class 1X and 2X-PPP principal-only components will have a principal balance, which initially will equal zero. Interest will not accrue on any Class 1X or Class 2X-PPP principal-only component.

Solely for purposes of calculating distributions of principal and interest and the allocation of losses realized on the mortgage loans, the Class CA-1C Certificates will be deemed to be comprised of the Class CA-1C Group 1 Component and the Class CA-1C Group 2 Component. Each Class CA-1C Component will have a component principal balance representing the portion of the related class principal balance derived from the related loan group. Interest will be payable with respect to each Class CA-1C Component.

Interest to be distributed on the certificates (or added to the principal balance of the certificates in the form of Net Negative Amortization, as defined below) on any distribution date will consist of accrued and unpaid interest as of previous distribution dates and interest accrued during the period beginning on the 25th day of the preceding calendar month (or, in the case of the first distribution date, July 27, 2006) and ending on the 24th day of the month of that distribution date, except for the Class 2A, Class 2A-1B, Class 1X and Class 2X-PPP Certificates, which accrue interest during the preceding calendar month. Interest on the Class 1A, Class 1A-1B, Class CA-1C and Class B Certificates will be calculated based on the actual number of days in the certificate accrual period and assuming a 360 day year. Interest on the Class 2A, Class 2A-1B, Class 1X and Class 2X-PPP Certificates will be calculated based on a year consisting of twelve thirty-day months.

In the event that an increase in the applicable index causes interest to accrue on a mortgage loan for a given month in excess of the monthly payment for that mortgage loan, the excess interest will be added to the outstanding principal balance of that mortgage loan in the form of “negative amortization.” For any distribution date, the excess, if any, of (i) the aggregate amount of negative amortization with respect to all mortgage loans in a loan group for the calendar month prior to that distribution date, over (ii) the aggregate amount of prepayments in full and partial prepayments received with respect to all mortgage loans in that loan group during the related prepayment period (the “Net Negative Amortization”), will be deducted from interest payable to the related certificates as described in “Description of the Certificates—Distributions of Interest” in this prospectus supplement. The amount deducted from the interest payable to each class of certificates will be added to the principal balance of that class.

It is possible that, on any given distribution date, there will be insufficient payments from the mortgage loans to make the interest distributions (net of any Net Negative Amortization deducted from interest payable) described in this prospectus supplement. If the servicer does not advance its own funds, because it determines that the advance would be nonrecoverable, some certificates, most likely the subordinate certificates, may not receive the full amount of accrued interest to which they are entitled. If this happens, those certificates will be entitled to receive any shortfall in interest distributions on future distribution dates in the same priority as their distribution of current interest. However, there will be no extra interest paid on that shortfall.

The amount of interest each Class CA-1C Component, the Class 1A and Class 1A-1B Certificates and each class of Class B Certificates accrues during each certificate accrual period will equal a ratio, the numerator of which is the actual number of days in that accrual period and the denominator of which is 360, multiplied by the annual certificate interest rate in effect for that

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accrual period for that class or component and multiplied by the related class principal balance or component principal balance. The amount of interest the Class 2A and Class 2A-1B Certificates accrue during each certificate accrual period will equal 1/12th of the annual certificate interest rate in effect for that accrual period for that class multiplied by their respective class principal balance. The principal balance used for this calculation for the Class A and Class B Certificates on the first distribution date will be the applicable principal balance as of July 27, 2006, which is the closing date. The principal balance used for this calculation on each distribution date thereafter will be the applicable principal balance immediately after the preceding distribution date. For a description of how the interest distributions to the Class 1X and Class 2X-PPP Certificates are determined, see “Description of the Certificates—Distributions of Interest” in this prospectus supplement. The annual certificate interest rate for each class of offered certificates is described on pages S-6 to S-12 of this prospectus supplement.

No interest will accrue on the Class 1X or Class 2X-PPP principal-only components.

One-Year MTA Certificates. The certificate interest rates for the Class 2A and Class 2A-1B Certificates adjusts monthly based on an index (currently the One-Year MTA, as described in “Description of the Mortgage Pool—The Indexes” in this prospectus supplement). The formulas for the calculation of the certificate interest rates for the Class 2A and Class 2A-1B Certificates appear in the notes to the table on page S-6 of this prospectus supplement. However, the certificate interest rates for these classes of certificates are subject to caps described the notes to the table on page S-6 of this prospectus supplement.

For the initial distribution date only, the Class 2A and Class 2A-1B Certificates may receive as interest, in addition to interest accrued at their certificate interest rates, carryover shortfall amounts, as described in “Description of the Certificates—Distributions of Interest—Carryover Shortfall Amount” in this prospectus supplement. The Class 2A and Class 2A-1B Certificates will not receive any carryover shortfall payments on any other distribution date. For more information, see “Risk Factors—The Class 2A and Class 2A-1B Certificates May Receive Interest at a Certificate Interest Rate Lower than One-Year MTA Index Plus the Related Margin”, “Description of the Mortgage Pool—The Indexes” and “Description of the Certificates—Distributions of Interest” in this prospectus supplement.

LIBOR Certificates. The certificate interest rates for the Class 1A, Class 1A-1B, Class CA-1C and Class B Certificates adjust monthly based on the average of quotations of the London Interbank Offered Rate for one-month U.S. dollar deposits, or LIBOR, as described in “Description of the Certificates—Calculation of LIBOR” in this prospectus supplement. The formulas for the calculation of the certificate interest rates for these LIBOR Certificates appear in the notes to the table on page S-6 of this prospectus supplement. However, the certificate interest rates for these classes of certificates (or the components thereof) are subject to caps described the notes to the table on page S-6 of this prospectus supplement.

On each distribution date, the Class 1A, Class 1A-1B, Class CA-1C and Class B Certificates may receive as interest, in addition to interest accrued at their certificate interest rates, carryover shortfall amounts, as described in “Description of the Certificates—Distributions of Interest—Carryover Shortfall Amount” in this prospectus supplement.

Interest otherwise available for distribution to the Class 1X and Class 2X-PPP Certificates on any distribution date may be reduced by carryover shortfall amounts payable to the Class A and Class B Certificates, as described in “Description of the Certificates—Distributions of Interest—Carryover Shortfall Amounts” in this prospectus supplement.

Compensating Interest and Interest Shortfalls

Prepayments in Full. When mortgagors make prepayments in full, they need not pay a full month's interest. Instead, they are required to pay interest only to the date of their prepayment. To compensate certificateholders for the shortfall in interest this causes, the servicer may pay compensating interest to the certificateholders out of the servicing fee it collects, as well as from certain other sources. For a description of how compensating interest is allocated among the certificates as well as important limitations on the amount of compensating interest that will be allocated among the certificates, see “Description of the Certificates—Distributions of Interest—Compensating Interest” and “Yield and

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Prepayment Considerations” in this prospectus supplement.

Partial Prepayments. When mortgagors make partial prepayments, they do not pay interest on the amount of that prepayment. Certificateholders will receive no compensating interest to compensate them for the shortfall in interest this causes.

Distributions of Principal

General. As the mortgagors pay principal on the mortgage loans in each loan group, that principal is passed on to the holders of the certificates related to that loan group.

The Class A Certificates and (in the event Net Negative Amortization has been allocated to the Class 1X or Class 2X-PPP Certificates) the Class 1X and Class 2X-PPP Certificates, in the aggregate, generally will receive their pro rata share of scheduled principal payments received on the mortgage loans in the related loan group on each distribution date. In addition, unless credit enhancement to the Class A, Class 1X and Class 2X-PPP Certificates has reached a specified level and the delinquencies and losses on the mortgage loans in the related loan group do not exceed specified limits, the Class A, Class 1X and Class 2X-PPP Certificates, in the aggregate, generally will receive 100% of all principal prepayments received on the mortgage loans in the related loan group, net of any portion thereof applied to reduce negative amortization, until the tenth anniversary of the first distribution date, after which they will receive a disproportionately large, but decreasing, share of principal prepayments.

Certificates Related to Loan Group 1: On each distribution date, a portion of the principal received or advanced on the mortgage loans in loan group 1 will be distributed, first, to the Class 1A and Class 1A-1B Certificates and the Class CA-1C Group 1 Component, pro rata, and, second, to the Class 1X Certificates, as described in “Description of the Certificates—Distributions of Principal—Group 1 Senior Principal Distribution Amount” in this prospectus supplement. However, not all of these certificates will receive principal on each distribution date. See Appendix A for a table showing, for each class of these certificates (other than the Class 1X Certificates), the rate of return of principal that would result from different rates of prepayments on the mortgage loans in loan group 1. However, if the Class B Certificates are no longer outstanding, then the Class 1A, Class 1A-1B and Class 1X Certificates and the Class CA-1C Group 1 Component will not receive principal in the order of priority described in “Description of the Certificates—Distributions of Principal—Group 1 Senior Principal Distribution Amount” in this prospectus supplement. Instead, each of these classes of certificates will generally receive principal pro rata according to its class principal balance or related component principal balance, as applicable. If the Class B Certificates are outstanding, the Class 1X Certificates will not receive any distributions of principal until the principal balances of the Class 1A and Class 1A-1B Certificates and the Class CA-1C Group 1 Component have each been reduced to zero.

Certificates Related to Loan Group 2: On each distribution date, a portion of the principal received or advanced on the mortgage loans in loan group 2 will be distributed, first, to the Class 2A and Class 2A-1B Certificates and the Class CA-1C Group 2 Component, pro rata, and, second, to the Class 2X-PPP Certificates, as described in “Description of the Certificates—Distributions of Principal—Group 2 Senior Principal Distribution Amount” in this prospectus supplement. However, not all of these certificates will receive principal on each distribution date. See Appendix A for a table showing, for each class of these certificates (other than the Class 2X-PPP Certificates), the rate of return of principal that would result from different rates of prepayments on the mortgage loans in loan group 2. However, if the Class B Certificates are no longer outstanding, then the Class 2A, Class 2A-1B and Class 2X-PPP Certificates and the Class CA-1C Group 2 Component will not receive principal in the order of priority described in “Description of the Certificates—Distributions of Principal—Group 2 Senior Principal Distribution Amount” in this prospectus supplement. Instead, each of these classes of certificates will generally receive principal pro rata according to its class principal balance or related component principal balance, as applicable. If the Class B Certificates are outstanding, the Class 2X-PPP Certificates will not receive any distributions of principal until

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the principal balances of the Class 2A and Class 2A-1B Certificates and Class CA-1C Group 2 Component have each been reduced to zero.

Class B Certificates. On each distribution date, the Class B-1, Class B-2, Class B-3, Class B-4, Class B-5, Class B-6, Class B-7, Class B-8, Class B-9, Class B-10, Class B-11, Class B-12, Class B-13 and Class B-14 Certificates will be entitled to receive a portion of the scheduled principal received or advanced on the mortgage loans in loan groups 1 and 2, pro rata, according to their respective class principal balances. Unless credit enhancement to the related senior certificates has reached a specified level and the delinquencies and losses on the mortgage loans do not exceed specified limits, the Class B Certificates generally will receive a portion of the principal prepayments on the mortgage loans only on and after the tenth anniversary of the first distribution date. However, under certain conditions described in this prospectus supplement under “Description of the Certificates—Priority of Distributions,” the amount of principal prepayments otherwise distributable to some classes of Class B Certificates (as defined in “Description of the Certificates—General” in this prospectus supplement) will instead be paid to other classes of these certificates with a higher priority.

Priority of Principal Distributions. Each class of certificates entitled to principal receives its principal entitlements in the order described in “Description of the Certificates—Priority of Distributions” in this prospectus supplement. It is possible that, on any given distribution date, there will be insufficient payments from the mortgage loans to make the principal distributions described in this prospectus supplement. As a result, some certificates, most likely the subordinate certificates, may not receive the full amount of principal distributions to which they are entitled.

The Class 1X and Class 2X-PPP Certificates will not receive any distributions of principal in respect of their interest-only components.

For a more detailed description of how distributions of principal will be allocated among the various classes of certificates, see “Description of the Certificates—Distributions of Principal” in this prospectus supplement.

Cross-Collateralization of Loan Group 1 and Loan Group 2

In certain limited circumstances, principal and interest collected from either of loan group 1 or loan group 2 may be used to pay principal or interest, or both, to the senior certificates unrelated to that loan group. See “Description of the Certificates—Cross-Collateralization” in this prospectus supplement.

The Class R Certificates

The Class R Certificates will receive $100 of principal on the first distribution date, as well as one month's interest on that amount. These certificates are not expected to receive any material distributions on any other distribution date. See “Description of the Certificates—The Class R Certificates” in this prospectus supplement. However, holders of the Class R Certificates may have tax liabilities that substantially exceed any distributions on those certificates. See “Yield and Prepayment Considerations—Additional Yield Considerations Applicable Solely to the Class R Certificates” and “Material Federal Income Tax Consequences—Special Tax Considerations Applicable to the Residual Certificates” in this prospectus supplement.

CREDIT ENHANCEMENTS

Subordination. The senior certificates will receive all distributions of interest and principal that they are entitled to receive on each distribution date before the subordinate certificates receive any distributions on that distribution date. This provides credit enhancement to the senior certificates. In a similar fashion, each class of subordinate certificates will provide credit enhancement to all other subordinate certificates with lower numerical class designations.

Shifting of Interests. The senior certificates generally will receive their pro rata share of scheduled principal payments received on the mortgage loans in the related loan group on each distribution date. In addition, unless credit enhancement to the senior certificates has reached a specified level and the delinquencies and losses on the mortgage loans in the related loan group do not exceed specified limits, the senior certificates in the aggregate will receive 100% of all principal prepayments received on the

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mortgage loans in the related loan group, net of any portion thereof applied to reduce negative amortization, until the tenth anniversary of the first distribution date. During the next four years the senior certificates in the aggregate will generally receive a disproportionately large, but decreasing, share of principal prepayments on the mortgage loans in the related loan group. This will result in a quicker return of principal to the senior certificates and increases the likelihood that holders of the senior certificates will be paid the full amount of principal to which they are entitled.

For a more detailed description of how principal prepayments are allocated among the senior certificates and the subordinate certificates, see “Description of the Certificates—Principal Prepayments” in this prospectus supplement.

ALLOCATION OF LOSSES

Realized Losses. A loss is realized on a mortgage loan when the servicer determines that it has received all amounts it expects to recover for that mortgage loan and the amounts are less than the outstanding principal balance of the mortgage loan and its accrued and unpaid interest. Losses will be allocated to the certificates by deducting the losses from the principal balance of the certificates without making any payments to the certificateholders. The amount of losses will be allocated to the most junior class of subordinate certificates related to the loan group that suffered those losses then outstanding. Losses will be allocated to the senior certificates other than the Class R Certificates only after the principal balances of all of the subordinate certificates have been reduced to zero. After the principal balances of all of the subordinate certificates have been reduced to zero, (i) any loss with respect to a mortgage loan in loan group 1 will be allocated (a) first, to the Class CA-1C Certificates, to its Class CA-1C Group 1 Component, until such component principal balance has been reduced to zero; (b) second, to the Class 1A-1B Certificates, until its class principal balance has been reduced to zero; and (c) third, to the Class 1A and Class 1X Certificates, pro rata according to class principal balance, until their respective class principal balances have each been reduced to zero and (ii) any loss with respect to a mortgage loan in loan group 2 will be allocated (a) first, to the Class CA-1C Certificates, to its Class CA-1C Group 2 Component, until such component principal balance has been reduced to zero; (b) second, to the Class 2A-1B Certificates, until its class principal balance has been reduced to zero; and (c) third, to the Class 2A and Class 2X-PPP Certificates, pro rata according to class principal balance, until their respective class principal balances have each been reduced to zero.

OPTIONAL TERMINATION

When the aggregate principal balance of the mortgage loans owned by the Trust has been reduced to less than 10% of that balance as of the Cut-Off Date, the servicer may purchase all of the mortgage loans owned by the Trust, which will result in the termination of the Trust. See “Description of the Certificates—Optional Termination of the Trust” in this prospectus supplement.

YIELD CONSIDERATIONS

The yield to maturity on each class of certificates will depend upon, among other things:

The Class 1X and Class 2X-PPP Certificates, which generally receive only distributions of interest (except for amounts added to their class principal balance as a result of the allocation of Net Negative Amortization, which is then distributed to those Class X Certificates as principal), will be especially sensitive to the rate of prepayments on the related mortgage loans. For a discussion of special yield considerations applicable to these certificates, see “Risk Factors” and “Yield and Prepayment Considerations—Yield Considerations with Respect to the Class X Certificates” in this prospectus supplement.

See “Yield and Prepayment Considerations” in this prospectus supplement.

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BOOK-ENTRY REGISTRATION

In general, the offered certificates, other than the Class R Certificates, will be available only in book-entry form through the facilities of The Depository Trust Company, Euroclear and Clearstream. See “Description of the Securities—Form of Securities” in the accompanying prospectus.

DENOMINATIONS

The offered certificates, other than the Class X and Class R Certificates, are offered in minimum denominations of $25,000 each and multiples of $1 in excess of $25,000.

The Class X Certificates are offered in minimum denominations of $100,000 initial class notional amount each and multiples of $1 in excess of $100,000.

The Class R Certificates will have an initial class principal balance of $100 and will be offered in a single certificate that represents a 99.99% interest in its class.

LEGAL INVESTMENT

As of the date of their issuance, all of the offered certificates, other than the Class B-6, Class B-7, Class B-8, Class B-9, Class B-10 and Class B-11 Certificates, will be “mortgage related securities” for purposes of the Secondary Mortgage Market Enhancement Act of 1984. See “Certain Legal Investment Aspects” in this prospectus supplement for important information concerning possible restrictions on ownership of the offered certificates by regulated institutions. You should consult your own legal advisors in determining whether and to what extent the offered certificates constitute legal investments for you.

ERISA CONSIDERATIONS

Subject to important considerations described under “ERISA Considerations” in this prospectus supplement and in the accompanying prospectus, the offered certificates, other than the Class 2X-PPP and Class R Certificates, will be eligible for purchase by persons investing assets of employee benefit plans or individual retirement accounts. See “ERISA Considerations” in this prospectus supplement and in the accompanying prospectus.

FEDERAL INCOME TAX CONSEQUENCES

For federal income tax purposes, the servicer will cause three REMIC elections to be made with respect to the Trust. The certificates, other than the Class R Certificates, will represent ownership of REMIC regular interests, and will generally be treated as representing ownership of debt for federal income tax purposes. You will be required to include in income all interest and original issue discount on these certificates in accordance with the accrual method of accounting regardless of your usual methods of accounting. In addition, the Class 2X-PPP Certificates will also represent a right to receive certain prepayment penalties paid with respect to certain mortgage loans in loan group 2. For federal income tax purposes, the Class R Certificates will represent ownership of the REMIC residual interest. The portions of the Class 2X-PPP Certificates that represent a right to receive certain prepayment penalties will represent stripped interests in the mortgage loans to which they relate and will not represent an interest in any REMIC.

For further information regarding the federal income tax consequences of investing in the offered certificates, including important information regarding the tax treatment of the Class R Certificates, see “Material Federal Income Tax Consequences” in this prospectus supplement and in the accompanying prospectus.

RATINGS

It is a condition to the issuance of the offered certificates that they receive the following ratings from Standard & Poor's Ratings Services, a division of The McGraw-Hill Companies, Inc., and Moody's Investors Service, Inc.:

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The ratings on the offered certificates address the likelihood of the receipt by holders of the offered certificates of all distributions on the underlying mortgage loans to which they are entitled. They do not address the likely actual rate of prepayments. The rate of prepayments, if different than originally anticipated, could adversely affect the yield realized by holders of the offered certificates or cause the holders of the Class X Certificates to fail to recover their initial investment. The ratings assigned to the Class 2X-PPP Certificates do not address any assessment of the likelihood or frequency of prepayments on the related mortgage loans or the likelihood of receipt of prepayment penalty payments.

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RISK FACTORS

      The offered certificates are not suitable investments for all investors. In particular, you should not purchase any class of offered certificates unless you understand and are able to bear the prepayment, credit, liquidity and market risks associated with that class.

      The offered certificates are complex securities and it is important that you possess, either alone or together with an investment advisor, the expertise necessary to evaluate the information contained in this prospectus supplement and the accompanying prospectus in the context of your financial situation.

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THE SPONSOR

General

      Washington Mutual Mortgage Securities Corp., the sponsor of the securitization transaction, is a Delaware corporation and a wholly owned subsidiary of Washington Mutual Bank and an indirect wholly-owned subsidiary of Washington Mutual, Inc. At March 31, 2006, Washington Mutual, Inc. and its subsidiaries had assets of $348.7 billion. The sponsor engages in the business of (i) purchasing mortgage loans on a servicing retained and servicing released basis, (ii) selling mortgage loans in whole loan transactions and securitizing mortgage loans through affiliated and unaffiliated depositors, (iii) master servicing mortgage loans, (iv) acting as administrative agent of Washington Mutual Bank and its affiliates with respect to mortgage loans serviced by Washington Mutual Bank and its affiliates and (v) providing securitization services. The sponsor generally acts as master servicer or administrative agent with respect to all mortgage loans securitized by the sponsor.

      Securitization of mortgage loans is an integral part of the sponsor's conduit program. It has engaged in securitizations of first lien single-family residential mortgage loans through WaMu Asset Acceptance Corp., as depositor, since 2005, and has acted as its own depositor from 1979 until 2005.

      The sponsor participated with the underwriter in structuring the securitization transaction.

      The following table shows, for each indicated period, the aggregate principal balance of first lien single-family residential mortgage loans purchased by the sponsor during that period (except mortgage loans purchased in its capacity as depositor from an affiliated sponsor) and the portion of those mortgage loans securitized during that period in securitization transactions for which it or WaMu Asset Acceptance Corp. acted as depositor.

The Sponsor's Purchase and Securitization of Single-Family Residential Mortgage Loans

The Sponsor's Origination Channels

      All of the mortgage loans owned by the Trust have been purchased by the sponsor either from Washington Mutual Bank or from approved mortgage loan sellers. Through the sponsor's conduit program, the sponsor purchases mortgage loans in bulk from approved mortgage loan sellers on both a servicing retained and servicing released basis. In initially approving a mortgage loan seller, the sponsor takes into account the following: annual origination volume, tenure of business and key staff in originating loans, policies and procedures for originating loans including quality control and appraisal review, review audits performed on mortgage loan seller by rating agencies, regulatory agencies and government sponsored entities, the mortgage loan seller's financial statements, errors and omissions insurance coverage and fidelity bond and liability insurance coverage. Approved mortgage loan sellers' financial statements, insurance coverage and new review audits are reviewed on an annual basis. Additionally, the sponsor performs a monthly ongoing performance review of previously purchased mortgage loans for trends in delinquencies, losses and repurchases. The mortgage loan sellers' underwriting guidelines are reviewed for consistency with the sponsor's credit parameters and conformity with the underwriting standards described under “Underwriting of the Mortgage Loans” below and are either approved or approved with exceptions. The mortgage loan sellers represent to the sponsor upon sale that the mortgage loans have been underwritten in accordance with the approved underwriting guidelines.

      The sponsor purchases some mortgage loans from Washington Mutual Bank. Washington Mutual Bank originates mortgage loans through its retail lending division, which is a network of its own banks and mortgage lending offices; through its ConsumerDirect lending division, which originates mortgage loans to

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employees of Washington Mutual Bank and its affiliates, originates mortgage loans through the internet and refinances mortgage loans held in Washington Mutual Bank's mortgage loan portfolio; and through its wholesale lending division, which is a network of independent mortgage loan brokers approved by Washington Mutual Bank. For each mortgage loan originated through Washington Mutual Bank's wholesale lending division, a mortgage loan broker submits a loan application package to Washington Mutual Bank for underwriting and funding, and receives a portion of the loan origination fee charged to the mortgagor at the time the loan is made. For some of the mortgage loans originated under Washington Mutual Bank's correspondent division, the correspondent lenders have delegated underwriting approval. Those correspondent lenders are authorized to underwrite mortgage loans with specified characteristics up to specified loan amounts, and must refer all other mortgage loans to Washington Mutual Bank for underwriting. In the case of mortgage loans underwritten by a correspondent lender, the correspondent lender will represent to Washington Mutual Bank that the mortgage loans have been underwritten in accordance with Washington Mutual Bank's underwriting guidelines. Correspondent lenders without delegated underwriting approval submit loan application packages to Washington Mutual Bank for underwriting and fund each loan only upon approval by Washington Mutual Bank.

STATIC POOL INFORMATION

      On May 15, 2006, the depositor filed with the Securities and Exchange Commission, as (i) Exhibits 99.1, 99.2, 99.3 and 99.4 to a Current Report on Form 8-K, static pool information about prior securitized pools and vintage pools of fixed-rate residential mortgage loans (non-traditional or “alternative A” underwriting standards) of the sponsor and (ii) Exhibits 99.9 and 99.10 to a Current Report on Form 8-K, static pool information about prior securitized pools of Option ARM Loans (non-traditional or “alternative A” underwriting standards) of the sponsor. The static pool information includes (i) information about the original characteristics of each prior securitized pool and vintage pool as of the cut-off date for that pool and (ii) delinquency, loss and prepayment information about each prior securitized pool and vintage pool in quarterly increments from the related cut-off date through March 31, 2006. The static pool information about prior securitized pools and vintage pools of the sponsor that were established before January 1, 2006 will not be deemed to be a part of this prospectus supplement, the accompanying prospectus or the related registration statement. “Option ARM Loans” are adjustable rate mortgage loans whose interest rates are tied to an index, which have an initial fixed-rate period of between one and twelve months, and which have a negative amortization feature.

      There can be no assurance that the rates of delinquencies, losses and prepayments experienced by the prior securitized pools and vintage pools will be comparable to delinquencies, losses and prepayments expected to be experienced by the mortgage loans owned by the Trust.

UNDERWRITING OF THE MORTGAGE LOANS

General

      All of the mortgage loans owned by the Trust have been originated in accordance with the underwriting standards of the sponsor or the underwriting guidelines of Washington Mutual Bank as described in this section. In addition, see “The Originators” in this prospectus supplement for additional information about the mortgage loans originated by Alliance Bancorp.

      The sponsor's underwriting standards and Washington Mutual Bank's underwriting guidelines generally are intended to evaluate the prospective borrower's credit standing and repayment ability and the value and adequacy of the mortgaged property as collateral. Some mortgage loans are manually underwritten, in which case an underwriter reviews a loan application and supporting documentation, if required, and a credit report of the borrower, and based on that review determines whether to originate a loan in the amount and with the terms stated in the loan application. Some mortgage loans may be underwritten through an automated underwriting system, including Washington Mutual Bank's automated underwriting system, described below.

      Prospective borrowers are required to complete a standard loan application in which they may provide financial information regarding such factors as their assets, liabilities and related monthly payments,

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income, employment history and credit history. Each borrower also provides an authorization to access a credit report that summarizes the borrower's credit history.

Evaluation of the Borrower's Credit Standing

      To evaluate a prospective borrower's credit history, the loan underwriter obtains a credit report relating to the borrower from one or more credit reporting companies, usually in the form of a merged credit report. The credit report typically contains information relating to such matters as credit history with local and national merchants and lenders, installment debt payments and any record of defaults, bankruptcy, repossession, suits or judgments. In most cases the credit report provides a credit score for the borrower, which represents a numerical weighing of the borrower's credit characteristics. Credit scores are designed to assess a borrower's creditworthiness and likelihood to default on an obligation over a defined period (usually two to three years) based on a borrower's credit history. Credit scores do not necessarily correspond to the probability of default over the life of a mortgage loan because they reflect past credit history, rather than an assessment of future payment performance. In addition, credit scores only indicate general creditworthiness, and credit scores are not intended to specifically apply to mortgage debt. Credit scores range from approximately 250 to approximately 900, with higher scores indicating more favorable credit history. If the loan underwriter obtains credit scores from three credit reporting companies, the middle score generally is used, and if two credit scores are obtained, the lowest score generally is used. In the case of co-borrowers, the credit score for the borrower with the lowest credit score generally is used (determined for each borrower as described in the immediately preceding sentence). Minimum credit scores are required for some loan products and loan programs. For borrowers for which credit scores are not available, the loan underwriter will require alternative documentation indicating the borrower's creditworthiness, such as rental or utility payment history or payment history on other debt.

Evaluation of the Borrower's Repayment Ability

      Under all documentation programs other than the no ratio programs and the no documentation programs, in evaluating a prospective borrower's ability to repay a mortgage loan, the loan underwriter considers the ratio of the borrower's mortgage payments, real property taxes and other monthly housing expenses to the borrower's gross income (referred to as the “housing-to-income ratio” or “front end ratio”), and the ratio of the borrower's total monthly debt (including certain non-housing expenses) to the borrower's gross income (referred to as the “debt-to-income ratio” or “back end ratio”). The maximum acceptable ratios may vary depending on other loan factors, such as loan amount and loan purpose, loan-to-value ratio, credit score and the availability of other liquid assets. Exceptions to the ratio guidelines may be made when compensating factors are present.

Evaluation of the Adequacy of the Collateral

      The adequacy of the mortgaged property as collateral generally is determined by an appraisal made in accordance with pre-established appraisal guidelines. At origination, all appraisals are required to conform to the Uniform Standards of Professional Appraisal Practice adopted by the Appraisal Standards Board of the Appraisal Foundation, and are made on forms acceptable to Fannie Mae and/or Freddie Mac. Appraisers may be staff appraisers employed by Washington Mutual Bank or independent appraisers selected in accordance with the pre-established appraisal guidelines. Such guidelines generally require that the appraiser, or an agent on its behalf, personally inspect the property and verify whether the property is in adequate condition and, if the property is new construction, whether it is substantially completed. However, in the case of mortgage loans underwritten through an automated underwriting system, an automated valuation model may be used, under which an appraiser does not inspect the property. In either case, the valuation normally is based upon a market data analysis of recent sales of comparable properties and, in some cases, a replacement cost analysis based on the current cost of constructing or purchasing a similar property. In the case of a streamline refinance, the appraisal guidelines may permit the property value obtained for an existing mortgage loan (or a mortgage loan which was previously refinanced) to be used. Title insurance is required for all mortgage loans, except that for mortgage loans secured by shares of cooperative apartments, title insurance is not required for the cooperative apartment building (but a lien

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search is provided by the title company). Specific additional title insurance coverage is required for some types of mortgage loans.

Documentation Programs

      Each mortgage loan has been underwritten under one of the following documentation programs. Under a full/alternative documentation program, a borrower's employment and income are verified. The employment and income as stated in the prospective borrower's loan application are verified either directly with the borrower's stated employer(s) or through receipt of alternative documentation such as the borrower's recent pay stub(s) and/or W-2 form(s) reflecting a minimum of 12 months of employment and income or, in the case of self-employed borrowers or borrowers who derive a substantial portion of their income from commissions, receipt of the borrower's personal (and, if applicable, business) tax returns. For self-employed borrowers, profit and loss statements may also be required. Generally, under a full/alternative documentation program, the borrower's stated assets are also verified either directly with the stated financial institution holding the stated asset or through receipt of alternative documentation such as the borrower's recent bank and/or brokerage statement(s). In addition, the borrower's employment may be verified with the employer by telephone or by other independent means.

      Generally, a reduced documentation program is available to borrowers with certain loan-to-value ratios, loan amounts, and credit scores. A reduced documentation program places increased reliance on the value and adequacy of the mortgaged property as collateral, the borrower's credit standing and (in some cases) the borrower's assets. Generally, under a reduced documentation program, either (i) a borrower's employment and assets are verified, but no verification of a borrower's income is undertaken, (ii) a borrower's employment and income are verified, but no verification of a borrower's assets is undertaken, or (iii) in the case of some rate/term and cash-out refinance mortgage loans, only the borrower's employment is verified. For mortgage loans underwritten under a reduced documentation program, less than 12 months of the borrower's income may be verified. Additionally, mortgage loans underwritten under a reduced documentation program may include mortgage loans originated as a “streamline” refinance if the lender originated the borrower's existing mortgage loan. In this case, the prospective borrower's income and assets either are not required to be obtained or are obtained but not verified, and the appraisal obtained for the existing mortgage loan (or a mortgage loan which was previously refinanced) may be used rather than a new appraisal. Eligibility criteria vary but may include minimum credit scores, maximum loan amounts, maximum debt-to-income ratios and specified payment histories on an existing mortgage loan (generally, a history of timely mortgage payments for the past twelve months, or for the duration of the mortgage loan if less than twelve months old) or on other debt. In all cases, the borrower's employment is verified with the employer by telephone or by other independent means.

      Generally, a no ratio program is available to borrowers with certain loan-to-value ratios, loan amounts, and credit scores. A no ratio program relies on the value and adequacy of the mortgaged property as collateral and the borrower's credit standing. The borrower's income is not required to be obtained or verified. Generally, under a no ratio program, the borrower's stated assets are also verified through receipt of the borrower's recent bank or brokerage statements or directly with the financial institution. In all cases, the borrower's employment is verified with the employer by telephone or by other independent means.

      Generally, a no documentation program is available to borrowers with certain loan-to-value ratios, loan amounts, and credit scores. A no documentation program relies on the value and adequacy of the mortgaged property as collateral and the borrower's credit standing. Generally, the borrower's employment, income and assets are neither obtained nor verified. In some cases, the borrower's employment may be verified by telephone with the employer or by other independent means if the borrower's employment has been disclosed.

Exceptions to Program Parameters

      Exceptions to the underwriting standards described above may be made on a case-by-case basis if compensating factors are present. In those cases, the basis for the exception is documented. Compensating factors may include, but are not limited to, low loan-to-value ratio, low debt-to-income ratio, good credit

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standing, the availability of other liquid assets, stable employment and time in residence at the prospective borrower's current address.

Automated Underwriting System

      Some mortgage loans may have been originated through Washington Mutual Bank's retail and wholesale lending divisions and have been underwritten in whole or in part through Washington Mutual Bank's proprietary automated underwriting system, known as Enterprise Decision Engine or “EDE”. Based on the borrower's credit report and the information in the borrower's loan application, the system either (a) approves the loan subject to the satisfaction of specified conditions, which may include the receipt of additional documentation, or (b) refers the loan application to an underwriter for manual underwriting. In making the underwriting decision, EDE distinguishes between ten different levels of credit standing, based on both the credit score and other items in the borrower's credit report. Washington Mutual Bank has developed these ten levels of credit standing based on a statistical analysis of the past performance of approximately 193,000 mortgage loans originated by Washington Mutual Bank for its own portfolio between 1998 and 2001. Washington Mutual Bank has been using EDE for underwriting of mortgage loans since January 2005. Washington Mutual Bank has also used in the past, and currently uses, other automated underwriting systems. All or some of the mortgage loans originated by Washington Mutual Bank may have been underwritten through EDE or another automated underwriting system.

Due Diligence

      The sponsor's credit risk oversight department conducts a credit, appraisal, and compliance review of adverse samplings (and, in some cases, statistical samplings) of mortgage loans prior to purchase from unaffiliated mortgage loan sellers. Sample size is determined by due diligence results for prior purchased pools from that seller, performance of mortgage loans previously purchased and characteristics of the pool presented for purchase. Automated valuation models are obtained on all mortgage loans purchased from unaffiliated sellers. For mortgage loans originated by Washington Mutual Bank, Washington Mutual Bank's credit risk oversight department conducts a quality control review of statistical samplings of originated mortgage loans on a regular basis.

THE ORIGINATORS

      The sponsor purchased the mortgage loans directly or indirectly from affiliated or unaffiliated third parties who either originated the mortgage loans or purchased the mortgage loans through correspondent or broker lending. The following unaffiliated third parties originated at least 10% of the mortgage loans (by aggregate principal balance as of Cut-Off Date): Alliance Bancorp, approximately 23.6%; First Horizon Home Loan Corporation, approximately 13.2%; Plaza Home Mortgage, Inc., approximately 11.0%; and Residential Funding Corporation, approximately 11.0%. No other unaffiliated third party originator originated more than 10% of the mortgage loans. All of the mortgage loans owned by the Trust have been originated in accordance with the underwriting standards of the sponsor. Below is information about Alliance Bancorp, including information about its origination program and origination experience.

Alliance Bancorp

      Alliance Bancorp is a California corporation. Alliance Bancorp is a leading residential mortgage banking company that focuses primarily on the origination and sale of “Prime Alt-A” mortgages. Prime Alt-A mortgages are mortgages made to borrowers whose credit is generally within Fannie Mae or Freddie Mac guidelines, but are considered “non-conforming” due to loan balances in excess of maximum conforming lending limits, limited or no documentation required for approval of the borrower. Alliance Bancorp's target Prime Alt-A mortgage borrowers consist of prime quality borrowers with high-end FICO scores, low loan-to-value ratios and non-conforming documentation. Alliance Bancorp has been originating mortgage loans since 1990 and Option ARM Loans since 2005. The principal executive offices of Alliance Bancorp are located at 1000 Marina Boulevard, Suite 100, Brisbane, CA 94005.

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      The following table reflects the Alliance Bancorp's originations of Option ARM Loans and total Alt-A originations for current year and previous two years:

THE DEPOSITOR

      WaMu Asset Acceptance Corp., the depositor, is a Delaware corporation and a wholly owned subsidiary of Washington Mutual Bank. The depositor engages in no activities other than securitizing assets. It will have no material continuing obligations with respect to the mortgage loans or the certificates following the issuance of the certificates, other than the obligations (i) to file financing statements perfecting the Trust's interest in the mortgage loans, (ii) to repurchase or substitute for affected mortgage loans in the event of a material breach of a representation and warranty made by the depositor in the pooling agreement that has not been remedied and (iii) to indemnify the underwriter against some civil liabilities, including liabilities under the Securities Act of 1933.

THE TRUST

General

      The issuer of the certificates, the Washington Mutual Mortgage Pass-Through Certificates WMALT Series 2006-AR6 Trust (the “Trust”), will be a statutory trust formed under the laws of the State of Delaware pursuant to a trust agreement between WaMu Asset Acceptance Corp., as depositor, and Christiana Bank & Trust Company, as Delaware trustee. The pooling and servicing agreement, dated as of the July 1, 2006 (the “pooling agreement”), among the depositor, Washington Mutual Bank, as servicer, the Delaware trustee and LaSalle Bank National Association, as trustee, will restate the trust agreement and will be the governing instrument of the Trust.

      The Trust will not own any assets other than the mortgage loans and the other assets described below. The Trust will not have any liabilities other than those incurred in connection with the pooling agreement and any related agreement. The Trust will not have any directors, officers or other employees. No equity contribution will be made to the Trust by the sponsor, the depositor or any other party, except for a de minimis contribution made by the depositor pursuant to the trust agreement, and the Trust will not have any other capital. The fiscal year end of the Trust will be December 31. The Trust will act through the trustee and the Delaware trustee, whose fees and reasonable expenses will be paid or reimbursed by the servicer.

Assignment of the Mortgage Loans and Other Assets to the Trust

      A pool of mortgage loans, as described in this prospectus supplement, will be sold to the Trust on July 27, 2006 (the “Closing Date”). The Trust will own the right to receive all scheduled monthly payments of principal and interest due on the mortgage loans after, and all principal prepayments collected on or after July 1, 2006, except with respect to (i) approximately 2.9% of the mortgage loans (by aggregate principal balance as of the Cut-Off Date, as defined in “Description of the Mortgage Pool” in this prospectus supplement) (the “August A Loans”) for which the Trust will be entitled to all scheduled monthly payments of principal and interest due on those August Loans after August 1, 2006 and all principal prepayments collected with respect to those August A Loans on or after July 12, 2006 and (ii) approximately 1.9% of the mortgage loans (by aggregate principal balance as of the Cut-Off Date, as defined in “Description of the Mortgage Pool” in this prospectus supplement) (the “August B Loans,” and together with the August A Loans, the “August Loans”) for which the Trust will be entitled to all

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scheduled monthly payments of principal and interest due on those August Loans after August 1, 2006 and all principal prepayments collected with respect to those August B Loans on or after July 14, 2006. A schedule to the pooling agreement will include information about each mortgage loan, including:

      The mortgage pool will be the primary asset of the Trust. The Trust will also contain other assets, including:

      In exchange for the mortgage loans and the other assets described above, the trustee will authenticate and deliver the certificates pursuant to the order of the depositor.

      It is the intent of the parties to the pooling agreement that the conveyance of the mortgage loans and the related assets to the Trust constitute an absolute sale of those assets. However, in the event that the pooling agreement for any reason is held or deemed to create a security interest in those assets, then the pooling agreement will constitute a security agreement and the depositor grants to the Trust a security interest in those assets. The depositor will file financing statements perfecting such security interest.

Restrictions on Activities of the Trust

      Pursuant to the pooling agreement, the Trust will have the power and authority (i) to acquire, hold, lease, manage, administer, control, invest, reinvest, operate and transfer assets of the Trust, (ii) to issue and make distributions on the certificates and (iii) to engage in such other activities as are described in the pooling agreement. The Trust will be required to act in accordance with requirements specified in the pooling agreement that are designed to maintain the Trust's existence as a legal entity separate and distinct from any other entity. The Trust will not be permitted to do any of the following:

      The permissible activities of the Trust may not be modified except by an amendment to the pooling agreement. See “Description of the Certificates—Amendment of the Pooling Agreement” in this prospectus supplement.

Discretionary Activities With Respect to the Trust

      The following is a description of material discretionary activities that may be taken with regard to the administration of the mortgage loans or the certificates:

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THE TRUSTEES

The Trustee

General

      LaSalle Bank National Association (“LaSalle”) will be the trustee under the pooling agreement. LaSalle is a national banking association formed under the federal laws of the United States of America. Its parent company, LaSalle Bank Corporation, is an indirect subsidiary of ABN AMRO Bank N.V., a Netherlands banking corporation. LaSalle has extensive experience serving as trustee on securitizations of residential mortgage loans. Since January 1994, LaSalle has served as trustee or paying agent on over 400 residential mortgage-backed security transactions involving assets similar to the mortgage loans. As of April 30, 2006, LaSalle serves as trustee or paying agent on over 300 residential mortgage-backed security transactions. The depositor and servicer may maintain other banking relationships in the ordinary course of business with the trustee. The trustee's corporate trust office is located at 135 South LaSalle Street, Suite 1625, Chicago, Illinois, 60603, Attention: Global Securities and Trust Services—Washington Mutual Mortgage Pass-Through Certificates WMALT Series 2006-AR6, or at such other address as the trustee may designate from time to time.

Material Duties of the Trustee

      The trustee will have the following material duties under the pooling agreement:

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      In its capacity as trustee, LaSalle will hold the mortgage loan files exclusively for the use and benefit of the Trust. LaSalle will not have any duty or obligation to inspect, review or examine any of the documents, instruments, certificates or other papers relating to the mortgage loans delivered to it to determine that the same are valid. The disposition of the mortgage loan files will be governed by the pooling agreement.

      LaSalle provides custodial services on over 1,000 residential, commercial and asset-backed securitization transactions and maintains almost 2.5 million custodial files in its two vault locations in Elk Grove, Illinois and Irvine, California. LaSalle's two vault locations can maintain a total of approximately 6 million custody files. All custody files are segregated and maintained in secure and fire resistant facilities in compliance with customary industry standards. The vault construction complies with Fannie Mae/Ginnie Mae guidelines applicable to document custodians. LaSalle maintains disaster recovery protocols to ensure the preservation of custody files in the event of force majeure and maintains, in full force and effect, such fidelity bonds and/or insurance policies as are customarily maintained by banks which act as custodians. LaSalle uses unique tracking numbers for each custody file to ensure segregation of collateral files and proper filing of the contents therein and accurate file labeling is maintained through a monthly quality assurance process. LaSalle uses a licensed collateral review system to track and monitor the receipt and movement internally or externally of custody files and any release or reinstatement of collateral.

Events of Default Under the Pooling Agreement

      In the event of a default by the servicer under the pooling agreement that has not been remedied, either the trustee or holders of certificates evidencing at least 25% of the voting rights will have the right to terminate the servicer. If the servicer is terminated, or the servicer resigns because its duties under the pooling agreement are no longer permitted under applicable law, the trustee will become the successor servicer. However, if the trustee is unwilling or unable to act as successor servicer, it may appoint, or petition a court to appoint, a successor servicer.

      The trustee will be required to notify certificateholders and the rating agencies of any event of a default by the servicer known to the trustee, and of the appointment of any successor servicer.

      In the event of a default by the depositor under the pooling agreement that has not been remedied, holders of certificates evidencing at least 25% of the voting rights will have the right to direct the trustee to institute a legal action to enforce the depositor's obligations under the pooling agreement.

      See “Description of the Securities—Events of Default Under the Governing Agreement and Rights Upon Events of Default” in the prospectus.

The Delaware Trustee

      Christiana Bank & Trust Company, the Delaware trustee under the pooling agreement, is a Delaware banking corporation. The Delaware trustee has served as Delaware trustee for asset-backed securities transactions involving first lien single-family residential mortgage loans since approximately January 2002.

      The Delaware trustee will serve as trustee for the Trust for the sole purpose of satisfying the requirement under the Delaware statutory trust statute that the Trust have at least one trustee with a principal place of business in Delaware. The Delaware trustee's duties under the pooling agreement will be limited to (i) accepting legal process served on the Trust in the State of Delaware and (ii) executing any

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certificates with respect to the Trust which the Delaware Trustee is required to execute under the Delaware statutory trust statute.

Limitations on the Trustees' Liability

      Neither the trustee nor the Delaware trustee will be liable under the pooling agreement:

      In the absence of bad faith, the trustee and the Delaware trustee may conclusively rely upon any certificates or opinions of counsel furnished to such trustee under the pooling agreement. Any such opinion of counsel will be full and complete authorization and protection in respect of any action taken or omitted to be taken by such trustee in good faith and in accordance with such opinion of counsel. Neither the trustee nor the Delaware trustee will be deemed to have knowledge or notice of any matter, including an event of default, unless actually known to it or unless it has received written notice thereof.

Resignation and Removal of the Trustees

      Each of the trustee and the Delaware trustee may at any time resign by giving written notice thereof to the servicer. Upon receiving such notice of resignation, the servicer will be required to appoint a successor trustee. If the trustee or the Delaware trustee ceases to be eligible under the pooling agreement and fails to resign, or if the trustee or the Delaware trustee becomes incapable of acting, the servicer may remove such trustee and appoint a successor trustee. The holders of certificates evidencing at least 50% of the voting rights may at any time remove the trustee or the Delaware trustee and appoint a successor trustee.

      Any expenses associated with the resignation of a trustee will be required to be paid by such trustee, and any expenses associated with the removal of a trustee will be required to be paid by the servicer.

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THE SERVICERS

General

      All of the mortgage loans owned by the Trust will be serviced by Washington Mutual Bank, as servicer, pursuant to the pooling agreement. Washington Mutual Mortgage Securities Corp. will act as administrative agent of the servicer with respect to the mortgage loans, pursuant to an administrative agent agreement between the administrative agent and the servicer. The administrative agent will be responsible for calculating monthly distributions on the certificates, preparing monthly distribution reports and other functions, as described under “—The Administrative Agent” below.

      The servicer will outsource to third party vendors some servicing functions, as described under “—The Servicer—The Servicer's Servicing Procedures—The Servicer's Third Party Vendors” below. The administrative agent will calculate monthly distributions to certificateholders and prepare monthly distribution reports using software licensed from a third party vendor and based on the third party vendor's model of the priority of distributions on the certificates.

      As of the Cut-Off Date, some of the mortgage loans had not yet had their servicing transferred to the servicer. These mortgage loans will be serviced by their respective originators or mortgage loan sellers on an interim basis until the servicing of such mortgage loans is transferred to the servicer. See “—Interim Servicing” below for more information.

The Servicer

The Servicer's Servicing Experience

      The servicer has been servicing single-family residential mortgage loans for over 100 years. The single-family residential mortgage loans serviced by the servicer have included, since 2001, sub-prime residential mortgage loans serviced for Long Beach Mortgage Company, an affiliate of the servicer, or for its securitization trusts.

      The following table shows the number and aggregate principal balance of single-family residential mortgage loans, including conforming and nonconforming mortgage loans and fixed rate and adjustable rate mortgage loans, and including prime and sub-prime mortgage loans, serviced by the servicer as of the specified date.

Single-Family Residential Prime and Subprime Mortgage Loans Serviced by the Servicer
(Dollar Amounts in Millions)

      The following table shows the number and aggregate principal balance of single-family residential mortgage loans, including conforming and nonconforming mortgage loans and fixed rate and adjustable rate mortgage loans (but excluding sub-prime mortgage loans), serviced by the servicer as of the specified date.

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Single-Family Residential Prime Mortgage Loans Serviced by the Servicer
(Dollar Amounts in Millions)

Servicing Procedures

      Servicing Functions. The functions to be performed by the servicer will include payment collection and payment application, investor reporting and other investor services, default management and escrow administration. The servicer will perform its servicing functions at loan servicing centers located in Florence, South Carolina; Milwaukee, Wisconsin; Northridge/Chatsworth, California; and Jacksonville, Florida.

      Servicing Standard; Waivers and Modifications. Pursuant to the pooling agreement, the servicer will be required to service the mortgage loans consistent with prudent mortgage loan servicing practices and (unless inconsistent with those servicing practices) in the same manner in which, and with the same care, skill, prudence and diligence with which, it services and administers similar mortgage loans for other portfolios. The servicer will be required to make reasonable efforts to collect or cause to be collected all payments under the mortgage loans and, to the extent consistent with the pooling agreement and applicable insurance policies, follow such collection procedures as are followed with respect to comparable mortgage loans that are held in portfolios of responsible mortgage lenders in the local areas where each mortgaged property is located.

      Consistent with the servicing standard described above, the servicer will be permitted to waive, modify or vary any term of any mortgage loan, subject to certain conditions, as described in “Description of the Securities—Collection and Other Servicing Procedures Employed by the Servicer, Manager, Bond Administrator or Certificate Administrator” in the prospectus.

      Mortgage Loan Servicing System. In performing its servicing functions, the servicer will use computerized mortgage loan servicing systems that it leases from Fidelity Information Services, a division of Fidelity National Financial (“Fidelity”), a third party vendor (collectively, the “Fidelity System”). The Fidelity System produces detailed information about the financial status of each mortgage loan, including outstanding principal balance, current interest rate and the amount of any advances, unapplied payments, outstanding fees, escrow deposits or escrow account overdrafts, and about transactions that affect the mortgage loan, including the amount and due date of each payment, the date of receipt of each payment (including scheduled payments and prepayments), and how the payment was applied. The Fidelity System also produces additional information about mortgage loans that are in default, including the amount of any insurance and liquidation proceeds received. The servicer began using the Fidelity System in 1996. Prior to July 2004, the servicer serviced some mortgage loans using a proprietary mortgage loan servicing system; in July 2004, the servicer consolidated servicing into a single servicing platform by converting approximately 1.2 million loan records from the proprietary mortgage loan servicing system to the Fidelity System.

      Custodial Account, Escrow Account, Investment Account and Certificate Account. Mortgagor payments on the mortgage loans, including scheduled monthly payments, any Curtailments and Payoffs and any escrow payments (which are payments made by some mortgagors and held by the servicer in escrow for future payment of taxes and insurance), will initially be deposited into either a lockbox account maintained by a third party financial institution or a payment clearing account maintained by the servicer. Payments deposited into the lockbox account will be transferred by the servicer into the payment clearing account. Other collections on the mortgage loans, including Liquidation Proceeds and Insurance Proceeds (each, as defined in the pooling agreement) (other than Insurance Proceeds required for the restoration or repair of the related mortgaged property, which the servicer will retain for such purpose), will also initially be deposited into a payment clearing account maintained by the servicer. Within 48 hours of

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