OREANDA-NEWS. S&P Global Ratings today lowered its ratings on 53 classes of mortgage pass-through certificates from 46 U. S. residential mortgage-backed securities (RMBS) transactions issued between 2003 and 2009 to 'D (sf)' (see list). At the same time, we placed one additional rating on CreditWatch with negative implications.

Today's downgrades reflect our assessment of the principal write-downs' impact on the affected classes during recent remittance periods. All of the classes whose ratings were lowered to 'D (sf)' today were rated either 'CCC (sf)' or 'CC (sf)' before today's rating action.

We also placed our 'CCC (sf)' rating on class 2-1A1 from MASTR Adjustable Rate Mortgages Trust 2007-3 on CreditWatch with negative implications because we are awaiting an explanation from the trustee regarding the nature of the principal write-downs to this class.

The 53 defaulted classes consist of the following:21 from prime jumbo transactions (38.89 %);13 from Alternative-A transactions (24.07 %);Eight from subprime transactions;Seven from negative amortization transactions;Two from resecuritized real estate mortgage investment conduit transactions;One from RMBS outside the guidelines transactions; andOne from a risk transfer transaction. All of the transactions in this review receive credit enhancement from a combination of subordination, excess spread, and overcollateralization (where applicable).

We will continue to monitor our ratings on securities that experience principal write-downs, and we will further adjust our ratings as we consider appropriate according to our criteria.