EXECUTION
      COPY


    


    EXCHANGE
      TRUST AGREEMENT

    


    This
      EXCHANGE TRUST AGREEMENT (this “Agreement”)
      dated
      as of September 1, 2007, is executed by and among Structured Asset Securities
      Corporation, as depositor (the “Depositor”)
      and
      U.S. Bank National Association, solely in its capacity as trustee pursuant
      to
      the Underlying Trust Agreement (as defined below) (the “Trustee”).

    


    WITNESSETH

    


    WHEREAS,
      the Depositor, the Trustee and Aurora Loan Services, LLC, as Master Servicer
      have entered into a Trust Agreement (the “Underlying
      Trust Agreement”)
      dated
      as of September 1, 2007 establishing Lehman XS Trust 2007-18N (the “Underlying
      Trust”);

    


    WHEREAS,
      the Underlying Trust has issued a series of certificates known as Mortgage
      Pass-Through Certificates, Series 2007-18N, evidencing the entire beneficial
      interest in the Underlying Trust;

    


    WHEREAS,
      the Exchange Classes and Exchangeable Class (each as defined herein) will be
      issued hereunder and will represent ownership interests in the Related REMIC
      Classes (as defined herein);

    


    WHEREAS,
      all or a portion of the Exchange Classes may be exchanged for the related
      Exchangeable Classes and vice versa; and

    


    WHEREAS,
      the parties hereto desire to create this Trust to issue the Exchange Classes
      and
      the Exchangeable Class subject to the terms and conditions set forth
      herein.

    


    NOW
      THEREFORE, the parties to this Agreement, in the several capacities hereinabove
      set forth, do hereby declare and establish this Agreement and do hereby
      undertake and otherwise agree as follows:

    


    ARTICLE
      I

    


    DEFINED
      TERMS

    


    Capitalized
      terms used and not defined herein shall have the respective meanings assigned
      to
      them in the Underlying Trust Agreement and the rules of construction set forth
      therein shall apply hereto. In addition, whenever used in this Agreement, the
      following words and phrases, unless the context otherwise requires, shall have
      the following meanings:

    


    “Aggregate
      Denomination”:
      As to
      any Class and date of determination, the aggregate of the denominations of
      the
      Outstanding Certificates of such Class on such date.

    


    “Authorized
      Officer”:
      The
      Chairman of the Board, the President or any Executive Vice President, Senior
      Vice President or Vice President.

    


    “Certificate”:
      A
      grantor trust pass-through security issued hereunder in a book-entry form as
      authorized by this Agreement.

    
      
         

      

      
         

        
          

        

      

      
         

      

    

    


    “Certificate
      Registrar”:
      For
      the purposes of this Agreement, the Trustee appointed pursuant to the Underlying
      Trust Agreement which shall act as Certificate Registrar under this Agreement
      subject to the terms and conditions and entitled to the same rights, protections
      and indemnities set forth in the Agreement.

    


    “Class”:
      Each
      Class of Certificates issued or issuable hereunder as set forth in Section
      2.02
      hereto and each REMIC Class issued under the Underlying Trust
      Agreement.

    


    “Class
      Balance”:
      With
      respect to any Exchangeable Class or Exchange Class, at any time, the aggregate
      of the Certificate Principal Amounts of all Outstanding Certificates of such
      Class.

    


    “Class
      Distribution Amount”:
      As to
      each Exchangeable Class and Exchange Class and any Distribution Date, an amount
      equal to the aggregate of the Class Interest Distribution Amount and Class
      Principal Distribution Amount on such date. As to each Related REMIC Class
      on
      any Distribution Date, the sum of (i) the interest distributable to such Class
      pursuant to the Underlying Trust Agreement on such date; and (ii) the amount
      of
      principal distributable to such Class pursuant to the Underlying Trust Agreement
      on such date.

    


    “Class
      Interest Distribution Amount”:
      As to
      each Exchangeable Class and Exchange Class, and each Distribution Date, an
      amount equal to interest distributable for such class.

    


    “Class
      Principal Distribution Amount”:
      As to
      each Exchangeable Class and Exchange Class, and each Distribution Date, an
      amount as to principal equal to (i) the concurrent distribution of principal
      in
      respect of each Related REMIC Class multiplied by (ii) a fraction, the numerator
      of which is the Aggregate Denomination of such Class and the denominator of
      which is the Initial Authorized Denomination of such Class.

    


    “Code”:
      The
      Internal Revenue Code of 1986, as amended, including any successor or amendatory
      provisions.

    


    “Combination
      Group”:
      Any
      allowable combination of Certificates as set forth on Appendix A.

    


    “Distribution
      Date”:
      As to
      any Exchangeable Class and Exchange Class, the Distribution Date for the Related
      REMIC Classes.

    


    “Exchange
      Classes”
or
      “Exchange
      Certificates”:
      Each
      Class of Certificates identified as such in Appendix A hereto and issued
      hereunder.

    


    “Exchangeable
      Classes”
or
      “Exchangeable
      Certificates”:
      Each
      Class of Certificates identified as such in Appendix A hereto and issued
      hereunder.

    


    “Initial
      Authorized Denomination”:
      With
      respect to any Class and Combination Group, the amount set forth with respect
      to
      such Class and such Combination Group in Appendix A under the heading “Maximum
      Balance” or “Maximum Original Balance.”

    


    “Issue
      Date”:
      September 28, 2007.

    
      
         

      

      
        2

        
          

        

      

      
         

      

    

    


    “Notional
      Amount”:
      With
      respect to any Notional Exchange Classes, as set forth in Appendix
      A
      hereto.

    


    “Notional
      Exchange Classes”:
      Not
      applicable.

    


    “Outstanding
      Certificate”:
      Any
      Outstanding Exchange Certificate and Outstanding Exchangeable
      Certificate.

    


    “Outstanding
      Exchangeable Certificate”:
      Any
      Exchangeable Certificate issued on the Issue Date; provided,
      however,
      that
      upon the exchange of any Exchangeable Certificate pursuant to Section 2.03
      hereof, the Exchangeable Certificate so exchanged shall be deemed no longer
      to
      be an Outstanding Certificate, and each Exchange Certificate issued in exchange
      therefor shall be deemed to be an Outstanding Exchange Certificate.

    


    “Outstanding
      Exchange Certificate”:
      Any
      Exchange Certificate issued on the Issue Date; provided,
      however,
      that
      upon the exchange of any Exchange Certificate pursuant to Section 2.03 hereof,
      the Exchange Certificate so exchanged shall be deemed no longer to be an
      Outstanding Exchange Certificate, and the Exchangeable Certificate issued in
      exchange therefor shall be deemed to be an Outstanding Exchangeable
      Certificate.

    


    “Paying
      Agent”:
      For
      the purposes of this Agreement, the Trustee appointed pursuant to the Underlying
      Trust Agreement which shall act as Paying Agent under this Trust Agreement
      subject to the same terms and conditions and entitled to the same rights,
      protections and indemnities set forth in the Underlying Trust
      Agreement.

    


    “Prospectus”:
      The
      prospectus dated August 16, 2007, as supplemented by a prospectus supplement
      dated September 27, 2007, relating to the Lehman XS Trust, Mortgage Pass-Through
      Certificates Series 2007-18N.

    


    “Realized
      Loss Allocation Amount”:
      As to
      each Exchangeable Class or Exchange Class and Distribution Date, an amount
      equal
      to the aggregate of the Realized Losses on such Distribution Date in respect
      of
      the Related REMIC Class or Classes multiplied by a fraction, the numerator
      of
      which is equal to the Aggregate Denomination of such Exchange or Exchangeable
      Class at the close of business on the related Record Date and the denominator
      of
      which is the Initial Authorized Denomination with respect to such Class.


    


    “Related
      REMIC Class”:
      As to
      any Exchange Class (and each Exchangeable Class of the same Combination Group),
      the REMIC Class with the identical class designation as such Exchange
      Class.

    


    “REMIC
      Class”
or
      “REMIC
      Certificates”:
      Each
      of the Underlying REMIC Certificates (as defined in the Underlying Trust
      Agreement).

    


    “Trust”:
      The
      trust created by this Agreement, the corpus of which consists of the Trust
      Fund.

    


    “Trust
      Account”:
      As
      defined in Section 3.02 hereof.

    
      
         

      

      
        3

        
          

        

      

      
         

      

    

    


    “Trust
      Fund”:
      The
      corpus of the trust created by this Agreement, consisting of the Trust Account
      and the uncertificated interests in the REMIC Certificates issued by the
      Underlying Trust and all payments thereon and all rights
      thereunder.

    


    “Underlying
      Trust”:
      As
      defined in the Preamble hereof.

    


    ARTICLE
      II

    


    THE
      TRUST

    


    Section
      2.01. Acceptance
      of REMIC Certificates.
      U.S.
      Bank National Association, acting in its capacity as Trustee, acknowledges
      the
      transfer and assignment to it of the uncertificated REMIC Certificates and
      hereby declares that it will hold the same in trust for the Certificateholders
      on the terms in this Agreement contained.

    


    Section
      2.02. Certificates.
      The
      Certificates authorized by this Agreement shall consist of each Exchange
      Class and Exchangeable Class having the characteristics specified or determined
      as provided in Appendix A and the Underlying Trust Agreement, and otherwise
      shall be subject to the terms and provisions set forth herein. 

    


    Section
      2.03. Exchanges.
      Certificates shall be exchangeable on the books of DTC, on and after the Closing
      Date, by notice to the Trustee and under the terms and conditions hereinafter
      set forth.

    


    In
      the
      case of each Combination Group, Exchange Certificates in such Combination Group
      shall be exchangeable for Exchangeable Certificates related to such Combination
      Group in respective denominations determined based on the proportion that the
      initial Certificate Principal Balances of such Exchange Certificates bear to
      the
      original Certificate Principal Balances of the related Exchangeable
      Certificates, as set forth in Appendix A. Upon any such exchange the portions
      of
      the Exchange Certificates designated for exchange shall be deemed cancelled
      and
      replaced by the Exchangeable Certificates issued in exchange therefor.
      Correspondingly, Exchangeable Certificates related to a Combination Group may
      be
      further designated for exchange for Certificates of the Exchange Classes in
      such
      Combination Group in respective denominations determined based on the proportion
      that the initial Certificate Principal Balances of such Exchangeable
      Certificates bear to the original Certificate Principal Balances of the related
      Exchange Certificates, as set forth in Appendix A. There shall be no limitation
      on the number of exchanges authorized pursuant to this Section 2.03, and, except
      as set forth below, no fee or other charge shall be payable to the Trustee
      or
      DTC in connection therewith.

    


    Upon
      the
      presentation and surrender by any Holder of its Certificates in the appropriate
      combination as set forth on Appendix A, such Holder shall hereunder transfer,
      assign, set over and otherwise convey to the Trustee, all of such Holder’s
      right, title and interest in and to such Certificates, including all payments
      of
      interest thereon received after the month of the date specified in the notice
      (as described in the immediately succeeding paragraph) relating to such
      exchange.

    
      
         

      

      
        4

        
          

        

      

      
         

      

    

    


    In
      order
      to effect an exchange of Certificates, the Certificateholder shall provide
      notice to the Trustee (substantially in the form of Exhibit I hereto) in writing
      or by e-mail at sfsexchange@usbank.com no
      later
      than two Business Days before the proposed exchange date. The exchange date
      may
      be any Business Day from and including the 25th
      day of
      the month to the second to the last Business Day of the month subject to the
      Trustee’s approval. The notice must be on the Certificateholder’s letterhead,
      carry a medallion stamp guarantee and set forth the following information:
      the
      CUSIP number of both Certificates to be exchanged and Certificates to be
      received; outstanding Certificate Balance or Notional Amount and the Original
      Certificate Balance or Notional Amount of the Certificates to be exchanged;
      the
      Certificateholder’s DTC participant number; and the proposed exchange date.
      After receiving the notice, the Trustee shall e-mail the Certificateholder
      with
      wire payment instructions relating to the exchange fee. A notice becomes
      irrevocable on the second Business Day before the proposed exchange
      date.

    


    Notwithstanding
      any other provision herein set forth, a fee shall be payable to the Trustee
      in
      connection with each exchange equal to $5,000 for each exchange
      request.

    


    The
      Trustee shall make the first distribution on an Exchange Certificate or an
      Exchangeable Certificate received in an exchange transaction on the Distribution
      Date in the following month to the Certificateholder of record as of the close
      of business on the last day of the month of the exchange.

    


    Section
      2.04. Delivery
      of Instruments.
      The
      Trustee shall furnish to each Holder, upon request, copies of this Agreement,
      without attachments, applicable to the Certificate(s) held by such
      Holder.

    


    ARTICLE
      III

    


    CERTIFICATES;
      DISTRIBUTIONS

    


    Section
      3.01. Issuance
      of Certificates.
      The
      Classes of Certificates issued hereunder shall be issued in book-entry form
      and
      shall be maintained in the names of the record owners thereof as entries on
      the
      books of DTC. Such Certificates shall be in authorized denominations set forth
      herein and in the Underlying Trust Agreement.

    


    Section
      3.02. Trust
      Account.
      On or
      before the Issue Date, the Trustee shall either (i) open with a depository
      institution one or more trust accounts in the name of the Trustee on behalf
      of
      the Trust Fund that shall collectively be the “Trust
      Account,”
      (ii) in lieu of maintaining any such account or accounts, maintain the
      Trust Account by means of appropriate entries on its books and records
      designating all amounts credited thereto in respect of the REMIC Certificates
      and all investments of any such amounts as being held by it in its capacity
      as
      Trustee for the benefit of the Holders of the Certificates or
      (iii) maintain the Trust Account in the form of any combination of accounts
      or book entries described in clauses (i) and (ii) above. Any manner or manners
      in which the Trust Account is maintained may at any time be changed without
      notice to, or the approval of Holders of, the Certificates so long as funds
      held
      in the Trust Fund by, or for the account of, the Trustee shall at all times
      be
      identified. To the extent that the Trust Account is maintained by the Trustee
      in
      the manner provided for in clause (ii) above, all references herein to deposits
      and withdrawals from the Trust Account shall be deemed to refer to credits
      and
      debits to the related books of the Trustee.

    
      
         

      

      
        5

        
          

        

      

      
         

      

    

    


    The
      Trustee shall deposit in the Trust Account all distributions in respect of
      the
      REMIC Certificates received by it as Trustee hereunder. All such distributions
      deposited from time to time in the Trust Account and all investments made with
      such moneys, including all income or other gain from such investments, shall
      be
      held by the Trustee in the Trust Account as part of the Trust Fund as herein
      provided, subject to withdrawal by the Trustee for distributions on the
      Certificates.

    


    Section
      3.03. Distributions.
      On each
      Distribution Date, the Trustee shall withdraw from the Trust Account the Class
      Distribution Amount for each Class and shall cause the Paying Agent to make
      the
      appropriate distributions to the Holders of each such Class. All distributions
      of such Class Distribution Amount that are made with respect to a particular
      Class shall be made pro
      rata
      among
      all Certificates of such class in proportion to their respective Certificate
      Balances, with no preference or priority of any kind. As among any Outstanding
      Exchange Classes, distributions shall be made to such Certificates, pro
      rata,
      in
      proportion to the Class Principal Balance of each such Class.

    


    Section
      3.04. Allocation
      of Realized Losses.
      On each
      Distribution Date, the Realized Loss Allocation Amount for each Exchange and
      Exchangeable Class shall be applied to such Class in reduction of the balances
      thereof.

    


    ARTICLE
      IV

    


    LIMITATION
      OF LIABILITY

    


    The
      Trustee shall be entitled to the same rights, protections and indemnities
      afforded to it under the Underlying Trust Agreement.

    


    



    
      
         

      

      
        6

        
          

        

      

      
         

      

    



    ARTICLE
      V

    


    THE
      TRUSTEE

    


    In
      the
      event that there shall be any matter arising under the Underlying Trust
      Agreement that requires the vote of Holders of Certificates outstanding
      thereunder, the Trustee shall vote such REMIC Certificates in such amounts
      and
      proportions as shall reflect instructions received from Holders of any
      Outstanding Exchange Certificates and Outstanding Exchangeable
      Certificates.

    


    ARTICLE
      VI

    


    TERMINATION

    


    The
      obligations and responsibilities of the Trustee shall terminate as to the Trust
      upon the same terms and conditions as the Underlying Trust pursuant to the
      Underlying Trust Agreement.

    


    ARTICLE
      VII

    


    SUPPLEMENTAL
      AGREEMENTS

    


    This
      Agreement may be amended or supplemented from time to time by the Depositor
      and
      the Trustee upon the same terms and conditions as the Underlying Trust Agreement
      may be amended or supplemented.

    


    ARTICLE
      VIII

    


    MISCELLANEOUS

    


    Section
      8.01. Certificateholders.
      The
      death or incapacity of any Certificateholder shall neither operate to terminate
      this Agreement, nor entitle such Certificateholder’s legal representative or
      heirs to claim an accounting or to take any action or proceeding in any court
      for a partition or winding-up of the affairs of the Trust Fund, nor otherwise
      affect the rights, duties and obligations of any of the parties to this
      Agreement.

    


    Except
      as
      provided in Article V and Article VII, no Certificateholder shall have any
      right
      to vote or in any manner otherwise control the operation and management of
      the
      Trust Fund or the obligations of the parties hereto, nor shall anything herein
      set forth, or contained in the terms of the Certificates, be construed so as
      to
      constitute the Certificateholders from time to time as partners or members
      of an
      association; nor shall any Certificateholder be under any liability to any
      third
      person by reason of any action taken by the parties to this Trust Agreement
      pursuant to any provision hereof.

    


    No
      Certificateholder shall have any right, by virtue of any provision of this
      Trust
      Agreement, to institute any suit, action or proceeding in equity or at law
      upon
      or under or with respect to this Agreement unless an Event of Default shall
      have
      occurred and be continuing in respect of this Agreement. It is understood and
      intended, and is expressly covenanted by each Certificateholder with every
      other
      Certificateholder and the Trustee, that no one or more Holders of Certificates
      shall have any right in any manner whatever by virtue of any provision of this
      Agreement to affect, disturb or prejudice the rights of the Holders of any
      other
      such Certificates, or to obtain or seek to obtain priority over or preference
      to
      any other such Holder, or to enforce any right under this Agreement, except
      in
      the manner herein provided and for the equal, ratable and common benefit of
      all
      Certificateholders. For the protection and enforcement of the provisions of
      this
      Section, each and every Certificateholder and the Trustee shall be entitled
      to
      such relief as can be given either at law or in equity.

    
      
         

      

      
        7

        
          

        

      

      
         

      

    

    


    Section
      8.02. Governing
      Law.
      THIS
      AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF
      THE
      STATE OF NEW YORK, WITHOUT REFERENCE TO ITS CONFLICT OF LAW PROVISIONS (OTHER
      THAN SECTION 5-1401 OF THE GENERAL OBLIGATIONS LAW), AND THE OBLIGATIONS, RIGHTS
      AND REMEDIES OF THE PARTIES HEREUNDER SHALL BE DETERMINED IN ACCORDANCE WITH
      SUCH LAWS.

    


    Section
      8.03. Demands,
      Notices and Communications.
      All
      formal demands, notices and communications by and among the Trustee, the
      Certificate Registrar, the Paying Agent and the Holder of any Certificate shall
      be in writing and delivered in person or by first class mail, postage prepaid,
      or by facsimile to the Trustee at its address or facsimile number set forth
      in
      the Underlying Trust Agreement. Any notice so mailed within the time prescribed
      in this Agreement shall be conclusively presumed to have been duly given whether
      or not the Person to whom such notice shall have been directed receives such
      notice.

    


    Section
      8.04. Severability
      of Provisions.
      If any
      one or more of the covenants, agreements, provisions or terms of this Trust
      Agreement shall be for any reason whatsoever held invalid, then such covenants,
      agreements, provisions or terms shall be deemed severable from the remaining
      covenants, agreements, provisions or terms of this Agreement and shall in no
      way
      affect the validity or enforceability of the other provisions of this Agreement
      or of the Certificates or the rights of the Holders thereof.

    


    Section
      8.05. Tax
      Status and Reporting.
      It is
      intended that the Trust Fund created hereunder be considered a “grantor trust”
under the Code. Based upon such characterization, within a reasonable period
      of
      time after the end of each calendar year but not later than the latest date
      permitted by law, the Trustee shall mail to each person who so requests in
      writing and who at anytime during such calendar year shall have been a
      Certificateholder the necessary information under applicable law for preparation
      of such Holder’s federal and state income tax returns unless substantially
      similar information has been previously provided to such
      Certificateholder.

    


    For
      federal income tax purposes, the grantor trust created hereunder shall have
      a
      calendar year taxable year. The Trustee shall prepare or cause to be prepared
      and shall file or cause to be filed with the Internal Revenue Service and
      applicable state or local tax authorities, income tax information returns for
      each taxable year with respect to the grantor trust.

    
      
         

      

      
        8

        
          

        

      

      
         

      

    

    


    IN
      WITNESS WHEREOF, the parties hereto hereby execute this Agreement, as of the
      day
      and year first above written.

     

    


     

    U.S.
      BANK
      NATIONAL ASSOCIATION

    solely
      in
      its capacity as Trustee

    


    By:_____________________________

    Name:___________________________

    Title:____________________________

    


    


    STRUCTURED
      ASSET SECURITIES CORPORATION

    in
      its
      capacity as Depositor

    


    By:______________________________

    Name:____________________________

    Title:_____________________________

    


     

    


     


    
      
         

      

      
        9

        
          

        

      

      
         

      

    



    APPENDIX
      A

     

    Available
      Exchange Combinations

    


    
      	
              Exchange
                Certificates

            	 	
              Exchangeable
                Certificates

            
	
              Combination

            	
              Maximum
                Initial 

              Principal
                Balance
                (1)

            	 	
              Class

            	
              Maximum
                Initial 

              Principal
                

              Balance
                (1)

            	
              Principal 

              Type

            	
              Interest
                Type

            	
              Interest
                Rate

            
	 	 	 	 	 	 	 	 
	
              Combination
                1

            	
               

            	 	 	 	 	 	 
	
              1-A2

            	
              $74,617,000

            	 	
              AF2

            	
              $142,135,000

            	
              Senior,
                Pass-through

            	
              Floating
                Rate

            	
              LIBOR
                + 1.000%(2)

            
	
              2-A2

            	
              $67,518,000

            	 	 	 	 	 	 


    

    


    


    
      	
              Exchange
                Certificates

            	 	
              Exchangeable
                Certificates

            
	
              Combination

            	
              Maximum
                Initial 

              Principal
                Balance
                (1)

            	 	
              Class

            	
              Maximum
                Initial 

              Principal
                

              Balance
                (1)

            	
              Principal
                

              Type

            	
              Interest
                Type

            	
              Interest
                Rate

            
	 	 	 	 	 	 	 	 
	
              Combination
                2

            	
               

            	 	 	 	 	 	 
	
              1-A3

            	
              $30,059,000

            	 	
              AF3

            	
              $57,258,000

            	
              Senior,
                Pass-through

            	
              Floating
                Rate

            	
              LIBOR
                + 1.250%(3)

            
	
              2-A3

            	
              $27,199,000

            	 	 	 	 	 	 


    

    


     

    (1)
      Exchange Certificates and Exchangeable Certificates in any combination may
      be
      exchanged only in the proportion that the maximum initial principal balances
      of
      such certificates bear to one another as shown above.

     

    (2)
      The
      Interest Rate is subject to the AF2 Net Funds Cap. After the Initial Optional
      Termination Date, the stated margin shall increase to two times its original
      value.

    


    (3)
      The
      Interest Rate is subject to the AF3 Net Funds Cap. After the Initial Optional
      Termination Date, the stated margin shall increase to two times its original
      value.

     

    



    
      
         

      

      
        A-1

        
          

        

      

      
         

      

    

    
 

    EXHIBIT
      I

    


    FORM
      OF EXCHANGE LETTER

    


     

    


    ___,
      20__

    


    


    U.S.
      Bank National Association

    One
      Federal Street, 3rd Floor

    Boston,
      Massachusetts 02110

    Attention:
      Corporate Trust Group, LXS 2007-18N

    


    


    
      	 	
              Re:

            	
              Lehman
                XS Trust 2007-18N,

            


    

    Mortgage
      Pass-Through Certificates, Series 2007-18N

     

    Ladies
      and Gentlemen:

    


    Pursuant
      to the terms of the Exchange Trust Agreement dated as of September 1, 2007
      (the
“Trust
      Agreement”),
      by
      and among Structured Asset Securities Corporation, as depositor and U.S. Bank
      National Association, as trustee (the “Trustee”),
      we
      hereby present and surrender the Certificates specified on Schedule
      I
      attached
      hereto and transfer, assign, set over and otherwise convey to the Trustee,
      all
      of our right, title and interest in and to such Certificates, including all
      payments of interest thereon received after [___________], 2007, in exchange
      for
      the related Certificates specified on Schedule
      I
      attached
      hereto. 

     

    We
      agree
      that upon such exchange the portions of the Certificates designated for exchange
      shall be deemed cancelled and replaced by the Certificates issued in exchange
      therefor. We confirm that we have paid a fee to the Trustee in connection with
      such exchange equal to $5,000.

    
 

     

    



    
      
         

      

      
        I-1

        
          

        

      

      
         

      

    



    Sincerely,

     

    


    By:  _____________________________

    Name:
      

    Title:
      

    


    Acknowledged
      by:

    


    U.S.
      BANK
      NATIONAL ASSOCIATION, 

    as
      Trustee

    


    


    By:  _____________________________

    Name:
      

    Title:

    


    


    



    
      
         

      

      
        I-2

        
          

        

      

      
         

      

    



    SCHEDULE
      I

    


    [insert
      the information as to the Exchange Class(es) and Exchangeable Class(es) to
      be
      exchanged required by Section 2.04 of the Trust Agreement]

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    
      
         

      

      
        I-3