Exhibit A Underlying Certificates Trust Asset Group Issuer Series Class Issue Date CUSIP Number Interest Rate Interest Type(1) Final Distribution Date Principal Type(1) Original Principal or Notional Balance of Class Underlying Certificate Factor(2) Principal or Notional Balance in the Trust Percentage of Class in Trust Approximate Weighted Average Coupon of Mortgage Loans Approximate Weighted Average Remaining Term to Maturity of Mortgage Loans (in months) Approximate Weighted Average Loan Age of Mortgage Loans (in months) Ginnie Mae I or II 2 Ginnie Mae   2007-033   AF(3) June 28, 2007 38375KFX5 (4) FLT June 2037 PT $187,781,333 0.99522012 $65,696,710 35.1537822985% 6.420% 356 4 II 3 Ginnie Mae   2007-037   FW(3) June 28, 2007 38375KNR9 (4) FLT June 2037 PT 230,357,142 0.99518017 99,518,017 43.4108528747 6.424 356 4 II 3 Ginnie Mae   2007-037   SN(3) June 28, 2007 38375KNK4 (4) INV/IO June 2037 NTL (PT) 230,357,141 0.99518017 99,518,017 43.4108530632 6.424 356 4 II 3 Ginnie Mae   2007-040   OA(3) July 30, 2007 38375KC67 0% PO June 2037 SC/PT 38,305,161 0.99745855 16,586,336 43.4108526525 6.424 356 4 II (1)  As defined under "Class Types" in Appendix I to the Base Offering Circular. (2)  Underlying Certificate Factors are as of August 2007. (3)  MX Certificates. (4)  These Underlying Certificates bear interest during their respective interest accrual periods, subject to the applicable maximum and minimum interest rates, as further described in the related Underlying Certificate Disclosure Documents, excerpts of which are attached as Exhibit B to this Supplement. A-1