The Association is authorized by section 306(g) of the National Housing Act (12 U.S.C. 1721(g)) upon such terms and conditions as it may deem appropriate, to guarantee the timely payment of principal of and interest on securities that are based on and backed by a trust or pool composed of mortgages which are insured or guaranteed by FHA, FmHA or VA. The Association's guaranty of mortgage-backed securities is backed by the full faith and credit of the United States. This subpart is limited to “modified pass-through” securities, and does not purport to set forth all the procedures and requirements that apply to the issuance and guaranty of such securities. All such transactions are governed by the specific terms and provisions of the Association's Mortgage-Backed Securities Guides (MBS Guides) and contracts entered into by the parties.