EXECUTION

    


    EXCHANGE
      TRUST AGREEMENT

    


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

    


    WITNESSETH

    


    WHEREAS,
      the Depositor, the Trustee, Aurora Loan Services, LLC, as Master Servicer and
      Risk Management Group, LLC, as credit risk manager, have entered into a Trust
      Agreement (the “Underlying
      Trust Agreement”)
      dated
      as of December 1, 2007 establishing BNC Mortgage Loan Trust 2007-4 (the
“Underlying
      Trust”);

    


    WHEREAS,
      the Underlying Trust has issued a series of certificates known as Mortgage
      Pass-Through Certificates, Series 2007-4, evidencing the entire beneficial
      interest in the Underlying Trust;

    


    WHEREAS,
      the Exchange Classes and Exchangeable Classes (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 Classes 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 Underlying Trust 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
      Distribution Amount”:
      As to
      each Exchange Class and Exchangeable Class and any Distribution Date, an amount
      equal to the aggregate of the Class Interest Distribution Amount and Class
      Principal Distribution Amount if any on such date. As to each Related REMIC
      Class on any Distribution Date, the sum of (i) the Current Interest and any
      Carryforward Interest (each as defined in the Underlying Trust Agreement)
      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 Exchange Class and Exchangeable Class, and each Distribution Date, an
      amount equal to the sum of (i) Current Interest and (ii) any Carryforward
      Interest (each as defined in the Underlying Trust Agreement) for such
      Class.

    


    “Class
      Principal Amount”:
      With
      respect to any Exchange Class or Exchangeable Class (other than any Notional
      Class), at any time, the aggregate of the Certificate Principal Amounts of
      all
      Outstanding Certificates of such Class. 

    


    “Class
      Principal Distribution Amount”:
      As to
      each Exchange Class and Exchangeable Class (other than any Notional Classes),
      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.

    


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

    


    “Exchange
      Options”:
      Any
      allowable exchanges of Certificates as set forth on Appendix A.

    


    “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.


    
      
        
        

      

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

    


    “Issue
      Date”:
      January 8, 2008.

    


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

    


    “Notional
      Exchangeable Classes”:
      Any of
      the Class A2B, Class A3B, Class A4B, Class M1B, Class M2B, Class M3B, Class
      M4B,
      Class M5B or Class M6B Certificates.

    


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

    


    “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.

    


    “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 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 November 26, 2007, as supplemented by a prospectus supplement
      dated January 8, 2008, relating to the BNC Mortgage Loan Trust, Mortgage
      Pass-Through Certificates Series 2007-4.

    


    “Realized
      Loss Allocation Amount”:
      As to
      each Exchange Class or Exchangeable 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 Exchange Option),
      the REMIC Class with the identical Class designation as such Exchange
      Class.


    
      
        
        

      

      
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    “REMIC
      Class”
or
      “REMIC
      Certificates”:
      Each
      of the following Classes of Certificates issued under the Underlying Trust
      Agreement in uncertificated form: the Class
      A2,
Class
      A3,
      Class A4, Class M1, Class M2, Class M3, Class M4, Class M5 and Class
      M6
Certificates.

    


    “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.

    


    “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.

    


    “Underwriting
      Agreement”:
      The
      Underwriting Agreement Standard Terms, dated as of December 21, 2005, as
      supplemented by the Terms Agreement, dated as of January 8, 2008, each by and
      between the Depositor and Lehman Brothers Inc.

    


    “WHFIT”:
      A
“widely held fixed investment trust” as that term is defined in Treasury
      Regulations section 1.671-5(b)(22) or successor provisions.

    


    “WHFIT
      Regulations”:
      Treasury Regulations section 1.671-5, as amended.

    


    “WHMT”:
      A
“widely held mortgage trust” as that term is defined in Treasury Regulations
      section 1.671-5(b)(23) or successor provisions.

    


    ARTICLE
      II

    


    THE
      TRUST

    


    Section
      2.01. Acceptance
      of REMIC Certificates.
      The
      Trustee acknowledges (i) the transfer and assignment to the Trustee of any
      uncertificated interests in the REMIC Certificates pursuant to Section 3.10
      of
      the Underlying Trust Agreement and (ii) any transfer and assignment of
      certificated 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 Exchange Option, Exchange Certificates in such Exchange Option
      shall be exchangeable for Exchangeable Certificates related to such Exchange
      Option in respective denominations determined based on the proportion that
      the
      initial Certificate Principal Amount of such Exchange Certificates bears to
      the
      original Certificate Principal Amount (or original Notional Amount in the case
      of Notional Exchangeable Classes) 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 an Exchange Option may be further
      designated for exchange for Certificates of the Exchange Classes in such
      Exchange Option in the respective denominations determined based on the
      proportion that the initial Certificate Principal Amount (or initial Notional
      Amount in the case of Notional Exchangeable Classes) of such Exchangeable
      Certificates bear to the original Certificate Principal Amount 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.


    
      
        
        

      

      
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    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.

    


    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 GCTSSPGTEAMC-1@wellsfargo.com, Rebecca.A.Lisi@wellsfargo.com
      and
      Scott.Runkles@wellsfargo.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 Principal Amount or Notional Amount and the
      original Certificate Principal Amount 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.


    
      
        
        

      

      
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    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.

    


    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 of Outstanding
      Exchange Certificates and Outstanding Exchangeable
      Certificates. 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
      Principal Amount (or Notional Amount, in the case of Notional Exchangeable
      Classes), with no preference or priority of any kind. 

    


    Section
      3.04. Allocation
      of Realized Losses.
      On each
      Distribution Date, the Realized Loss Allocation Amount for each Exchange Class
      and Exchangeable Class shall be applied to such Class in reduction of the Class
      Principal Amount (or Class Notional Amount, in the case of Notional Exchangeable
      Classes) thereof.


    
      
        
        

      

      
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    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.

    


    


    
      
        
        

      

      
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    ARTICLE
      V

    


    THE
      TRUSTEE

    


    In
      the
      event that the Trustee, as holder of the REMIC Certificates, is requested to
      vote in respect of 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; provided,
      that
      absent receipt of such instructions, the Trustee shall abstain from voting.
      The
      Trustee shall promptly notify the Holders of any outstanding Exchange
      Certificates of any such matter requiring their vote or consent.

    


    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 of 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 Agreement pursuant
      to any provision hereof.

    


    No
      Certificateholder shall have any right, by virtue of any provision of this
      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
      the
      Section, each and every Certificateholder and the Trustee shall be entitled
      to
      such relief as can be given either at law or in equity.


    
      
        
        

      

      
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    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 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.
      (a) It
      is the intended that the Trust Fund created hereunder be considered a “grantor
      trust” under the Code and a WHFIT that is a WHMT. The Trustee will report as
      required under the WHFIT Regulations to the extent such information as is
      reasonably necessary to enable the Trustee to do so is provided to the Trustee
      on a timely basis. The Trustee can assume that the DTC is the only middleman
      listed as the registered holder for the related Certificates. The Trustee shall
      not be liable for any tax reporting penalties that may arise under the WHFIT
      Regulations as a result of the Depositor incorrectly determining the status
      of
      the Trust Fund as a WHFIT.

    


    (b)
      The
      Trustee shall report required WHFIT information using the accrual method. The
      Trustee shall make available WHFIT information to holders annually. In addition,
      the Trustee will not be responsible or liable for providing subsequently
      amended, revised or updated information to any holder, unless requested by
      the
      holder.


    
      
        
        

      

      
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    (c)
      The
      Trustee shall not be liable for failure to meet the reporting requirements
      of
      the WHFIT Regulations nor for any penalties thereunder if such failure is due
      to: (i) the lack of reasonably necessary information being provided to the
      Trustee, (ii) incomplete, inaccurate or untimely information being provided
      to
      the Trustee or (iii) the inability of the Trustee, after good faith efforts,
      to
      alter its existing information reporting systems to capture information
      necessary to fully comply with the WHFIT Regulations for the 2008 calendar
      year.
      Each owner of a Certificate representing, in whole or in part, beneficial
      ownership of an interest in a WHFIT, by acceptance of its interest in such
      Certificate, will be deemed to have agreed to provide the Trustee with
      information regarding any sale of such Certificate, including the price, amount
      of proceeds and date of sale. Absent receipt of such information, and unless
      informed otherwise by the Depositor, the Trustee may assume there is no
      secondary market trading of WHFIT interests.

    


    (d)
      To
      the extent required by the WHFIT Regulations, the Trustee shall use reasonable
      efforts to publish on an appropriate website the CUSIPs for the Certificates
      that represent ownership of a WHFIT. The CUSIPs so published will represent
      the
      Rule 144A CUSIPs. The Trustee shall make reasonable good faith efforts to keep
      the website accurate and updated to the extent CUSIPs have been received. Absent
      the receipt of a CUSIP, the Trustee shall use a reasonable identifier number
      in
      lieu of a CUSIP. The Trustee shall not be liable for investor reporting delays
      that result from the receipt of inaccurate or untimely CUSIP
      information.

    


    (e)
      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.


    
      
        
        

      

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

     

    


     

    WELLS
      FARGO BANK, N.A.,

    solely
      in
      its capacity as Trustee

    


    By:        /s/
      Martin Reed        

    Name:        Martin
      Reed        

    Title:          Vice
      President      


    


    


    STRUCTURED
      ASSET SECURITIES

    CORPORATION,

    in
      its
      capacity as Depositor

    


    By:       /s/
      Nicholas Stimola        

    Name:       Nicholas
      Stimola        

    Title:         Vice
      President          

    


     

    


     


    
      
        
        

      

      
        11

        
          

        

      

      
        
        

      

    



    APPENDIX
      A

     

    


    Available
      Exchange Options

    

      
        	
                Exchange
                  Certificates

              	 	
                Exchangeable
                  Certificates

              
	
                Exchange
                  Options

              	
                Maximum
                  

                Initial
                  Principal 

                Balance
                  (1)

              	 	
                Class

              	
                Maximum
                  

                Initial
                  Principal 

                Balance/Initial
                  

                Notional
                  

                Amount(1)

              	
                Principal
                  Type

              	
                Interest
                  Type(2)

              
	 	 	 	 	 	 	 
	
                Exchange
                  Option 1

              	 	 	 	 	 	 
	
                A2

              	
                $45,455,000

              	 	
                A2A

              	
                $45,455,000

              	
                Senior,
                  Sequential Pay

              	
                Variable

              
	 	 	 	
                A2B

              	
                $45,455,000

              	
                Senior,
                  Interest-Only

              	
                Fixed
                  Rate

              
	
                Exchange
                  Option 2

              	 	 	 	 	 	 
	
                A3

              	
                $75,129,000

              	 	
                A3A

              	
                $75,129,000

              	
                Senior,
                  Sequential Pay

              	
                Variable

              
	 	 	 	
                A3B

              	
                $75,129,000

              	
                Senior,
                  Interest-Only

              	
                Fixed
                  Rate

              
	
                Exchange
                  Option 3

              	 	 	 	 	 	 
	
                A4

              	
                $96,481,000

              	 	
                A4A

              	
                $96,481,000

              	
                Senior,
                  Sequential Pay

              	
                Variable

              
	 	 	 	
                A4B

              	
                $96,481,000

              	
                Senior,
                  Interest-Only

              	
                Fixed
                  Rate

              
	
                Exchange
                  Option 4

              	 	 	 	 	 	 
	
                M1

              	
                $21,653,000

              	 	
                M1A

              	
                $21,653,000

              	
                Subordinated

              	
                Variable

              
	 	 	 	
                M1B

              	
                $21,653,000

              	
                Subordinated,
                  Interest-Only

              	
                Fixed
                  Rate

              
	
                Exchange
                  Option 5

              	 	 	 	 	 	 
	
                M2

              	
                $14,178,000

              	 	
                M2A

              	
                $14,178,000

              	
                Subordinated

              	
                Variable

              
	 	 	 	
                M2B

              	
                $14,178,000

              	
                Subordinated,
                  Interest-Only

              	
                Fixed
                  Rate

              
	
                Exchange
                  Option 6

              	 	 	 	 	 	 
	
                M3

              	
                $6,702,000

              	 	
                M3A

              	
                $6,702,000

              	
                Subordinated

              	
                Variable

              
	 	 	 	
                M3B

              	
                $6,702,000

              	
                Subordinated,
                  Interest-Only

              	
                Fixed
                  Rate

              
	
                Exchange
                  Option 7

              	 	 	 	 	 	 
	
                M4

              	
                $6,960,000

              	 	
                M4A

              	
                $6,960,000

              	
                Subordinated

              	
                Variable

              
	 	 	 	
                M4B

              	
                $6,960,000

              	
                Subordinated,
                  Interest-Only

              	
                Fixed
                  Rate

              
	
                Exchange
                  Option 8

              	 	 	 	 	 	 
	
                M5

              	
                $6,186,000

              	 	
                M5A

              	
                $6,186,000

              	
                Subordinated

              	
                Variable

              
	 	 	 	
                M5B

              	
                $6,186,000

              	
                Subordinated,
                  Interest-Only

              	
                Fixed
                  Rate

              
	
                Exchange
                  Option 9

              	 	 	 	 	 	 
	
                M6

              	
                $4,124,000

              	 	
                M6A

              	
                $4,124,000

              	
                Subordinated

              	
                Variable

              
	 	 	 	
                M6B

              	
                $4,124,000

              	
                Subordinated,
                  Interest-Only

              	
                Fixed
                  Rate

              


      

    

    


    


    
      	
              (1)

            	
              Exchange
                Certificates and Exchangeable Certificates in any Exchange Option
                shall be
                exchanged only in the proportion that the maximum initial principal
                balances or maximum initial notional amounts of such certificates
                bear to
                one another as shown above.

            


    

    
      	
              (2)

            	
              Subject
                to applicable net funds cap or adjusted net funds cap, as described
                in the
                Underlying Trust Agreement.

            


    

    


    



    
      
        
        

      

      
        A-1

        
          

        

      

      
        
        

      

    

     

    EXHIBIT
      I

    


    FORM
      OF EXCHANGE LETTER

    


    


    ___,
      20__

    


    


    Wells
      Fargo Bank, N.A.

    Sixth
      Street and Marquette Avenue

    Minneapolis,
      Minnesota 55479

    Attention:
      Corporate Trust Services, BNC
      2007-4

    


    


    
      	 	
              Re:

            	
              BNC
                Mortgage Loan Trust 2007-4,

            


    

    Mortgage
      Pass-Through Certificates, Series 2007-4

     

    Ladies
      and Gentlemen:

    


    Pursuant
      to the terms of the Exchange Trust Agreement dated as of December 1, 2007 (the
      “Trust
      Agreement”),
      by
      and among Structured Asset Securities Corporation, as depositor, and Wells
      Fargo
      Bank, N.A., 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:

    


    WELLS
      FARGO BANK, N.A., 

    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