26 CFR § 301.7701(i)-4 - Special rules for certain entities.
(a) States and municipalities -
(i) The entity is a State, territory, a possession of the United States, the District of Columbia, or any political subdivision thereof (within the meaning of § 1.103-1(b) of this chapter), or is empowered to issue obligations on behalf of one of the foregoing;
(2) Governmental purpose. The term governmental purpose means an essential governmental function within the meaning of section 115. A governmental purpose does not include the mere packaging of debt obligations for re-sale on the secondary market even if any profits from the sale are used in the performance of an essential governmental function.
(3) Determinations by the Commissioner. If an entity is not described in paragraph (a)(1) of this section, but has a similar purpose, then the Commissioner may determine that the entity is not classified as a taxable mortgage pool.
(b) REITs. [Reserved]
(c) Subchapter S corporations -
(1) In general. An entity that is classified as a taxable mortgage pool may not elect to be an S corporation under section 1362(a) or maintain S corporation status.
(2) Portion of an S corporation treated as a separate corporation. An S corporation is not treated as a member of an affiliated group under section 1361(b)(2)(A) solely because a portion of the S corporation is treated as a separate corporation under section 7701(i).