**Class X** Interest The Upper-Tier Regular Interest represented by the Class X Certificates as specified and described in the Preliminary Statement and the related footnote thereto.

**Class X** Certificates The Class X-A, Class X-B and Class X-D Certificates, as the context may require.

**Class X** Component Each of the Class X-A Components, the Class X-B Component and the Class X-D Component.

**Class X**-C Pass-Through Rate The Pass-Through Rate for Class X-C Certificates for any Distribution Date will be a per annum rate equal to the excess, if any, of (a) the Weighted Average Net Mortgage Rate for the related Distribution Date, over (b) the weighted average of the Pass-Through Rates of the Class C and Class D Certificates for such Distribution Date, weighted on the basis of their respective Certificate Balances immediately prior to that Distribution Date. The Pass-Through Rate applicable to the Class X-C Certificates for the initial Distribution Date shall be the rate set forth in the Preliminary Statement hereto.

**Class X**-B Pass-Through Rate The Pass-Through Rate for Class X-B Certificates for any Distribution Date will equal the excess, if any of (a) the Weighted Average Net Mortgage Rate for the related Distribution Date, over (b) the weighted average of the Pass-Through Rates of the Class A-S, Class B and Class C Certificates for such Distribution Date, weighted on the basis of their respective aggregate Certificate Balances immediately prior to the Distribution Date. The Pass-Through Rate applicable to the Class X-B Certificates for the initial Distribution Date shall be the rate set forth in the Preliminary Statement hereto.

**Class X** Pass-Through Rate With respect to each Class of Class X Certificates, for any Distribution Date, the excess, if any of (a) the Weighted Average Net Mortgage Rate for such Distribution Date, over (b) the weighted average of the Pass-Through Rates on the Underlying Classes of Principal Balance Certificates for such Distribution Date, weighted on the basis of their respective Certificate Balances immediately prior to such Distribution Date (or, with respect to any Class of Class X Certificates with one Underlying Class of Principal Balance Certificates, the Pass-Through Rate of such Underlying Class for such Distribution Date).

**Class X**-E Strip Rate With respect to the Class X-E Component for any Distribution Date, the (i) the WAC Rate for such Distribution Date over (ii) the Pass-Through Rate for the Corresponding Certificates.

**Class X**-A Pass-Through Rate The Pass-Through Rate for Class X-A Certificates for any Distribution Date will equal the excess, if any of (a) the Weighted Average Net Mortgage Rate for the related Distribution Date, over (b) the weighted average of the Pass-Through Rates on the Class A Certificates (other than the Class A-S Certificates) for such Distribution Date, weighted on the basis of their respective Certificate Balances immediately prior to the Distribution Date. The Pass-Through Rate applicable to the Class X-A Certificates for the initial Distribution Date shall be the rate set forth in the Preliminary Statement hereto.

**Class X**-D Pass-Through Rate The Pass-Through Rate for Class X-D Certificates for any Distribution Date will equal the excess, if any of (a) the Weighted Average Net Mortgage Rate for the related Distribution Date, over (b) the Pass-Through Rate of the Class D Certificates. The Pass-Through Rate applicable to the Class X-D Certificates for the initial Distribution Date shall be the rate set forth in the Preliminary Statement hereto.

**Class X**-G Pass-Through Rate The Pass-Through Rate for Class X-G Certificates for any Distribution Date will equal the excess, if any of (a) the Weighted Average Net Mortgage Rate for the related Distribution Date, over (b) the Pass-Through Rate of the Class G Certificates. The Pass-Through Rate applicable to the Class X-G Certificates for the initial Distribution Date shall be the rate set forth in the Preliminary Statement hereto.

**Class X**-F Pass-Through Rate The Pass-Through Rate for Class X-F Certificates for any Distribution Date will equal the excess, if any of (a) the Weighted Average Net Mortgage Rate for the related Distribution Date, over (b) the Pass-Through Rate of the Class F Certificates. The Pass-Through Rate applicable to the Class X-F Certificates for the initial Distribution Date shall be the rate set forth in the Preliminary Statement hereto.

**Class X**-E Pass-Through Rate The Pass-Through Rate for Class X-E Certificates for any Distribution Date will equal the excess, if any of (a) the Weighted Average Net Mortgage Rate for the related Distribution Date, over (b) the Pass-Through Rate of the Class E Certificates. The Pass-Through Rate applicable to the Class X-E Certificates for the initial Distribution Date shall be the rate set forth in the Preliminary Statement hereto.

**Class X**-2 Strip Rate With respect to (a) any Distribution Date through and including the August 2006 Distribution Date, the amount, if any, by which (i) the lesser of (x) the rate per annum corresponding to such Distribution Date as set forth in Schedule III hereto or (y) the Weighted Average Net Mortgage Rate for such Distribution Date exceeds (ii) the Class A-1 Pass-Through Rate for such Distribution Date and (b) any Distribution Date thereafter, zero.

**Class X**-A Strip Rate With respect to any Class of Class X-A Components for any Distribution Date, the (i) the WAC Rate for such Distribution Date over (ii) the Pass-Through Rate for the Corresponding Certificates.

**Class X**-D Certificate A Certificate designated as “Class X-D” on the face thereof, in the form of Exhibit A-1 hereto, and evidencing a “regular interest” in the Upper-Tier REMIC for purposes of the REMIC Provisions.

**Class X**-C Component The Component XD.

**Class X**-F Strip Rate With respect to the Class X-F Component for any Distribution Date, the (i) the WAC Rate for such Distribution Date over (ii) the Pass-Through Rate for the Corresponding Certificates.

**Class X**-C Strip Rate With respect to any Class of Class X-C Components for any Distribution Date, the (i) the Weighted Average Net Mortgage Pass Through Rate for such Distribution Date over (ii) the Pass-Through Rate for the Corresponding Certificates.

**Class X**-H Pass-Through Rate The Pass-Through Rate for Class X-H Certificates for any Distribution Date will equal the excess, if any of (a) the Weighted Average Net Mortgage Rate for the related Distribution Date, over (b) the Pass-Through Rate of the Class H Certificates for such Distribution Date. The Pass-Through Rate applicable to the Class X-H Certificates for the initial Distribution Date shall be the rate set forth in the Preliminary Statement hereto.

**Class X**-B Component The Class B Component, which constitutes a separate class of “regular interests”, within the meaning of Code Section 860G(a)(1), in the Upper-Tier REMIC with a pass-through rate equal to its Class X Strip Rate from time to time and a notional amount equal to its Component Notional Amount from time to time.

**Class X**-1 Strip Rate With respect to any Distribution Date, the amount, if any, by which (i) the Weighted Average Net Mortgage Rate for such Distribution Date exceeds (ii) the sum of the Class LA-1-2-A Component Class X-2 Strip Rate and the Class A-1 Pass-Through Rate for such Distribution Date.

**Class X**-D Strip Rate With respect to the Class X-D Component for any Distribution Date, the (i) the WAC Rate for such Distribution Date over (ii) the Pass-Through Rate for the Corresponding Certificates.

**Class X** Strip Rate With respect to each Component for any Distribution Date, a rate per annum equal to: (i) the WAC Rate for such Distribution Date, minus (ii) the Pass-Through Rate for the Corresponding Certificates.

**Class X**-F Component The Component XF.

**Class X**-D Component The Component XD.

**Class X**-H Certificate A Certificate designated as “Class X-H” on the face thereof, in the form of Exhibit A-1 hereto, and evidencing a “regular interest” in the Upper-Tier REMIC for purposes of the REMIC Provisions.