Role of the Conserved AAUAAA Sequence: Four AAUAAA Point Mutants Prevent Messenger RNA 3′ End Formation

A small region (220 bases) of SV40 sequence information—141 bases before the polyadenylation site and 79 beyond—are sufficient for cleavage of an messenger RNA precursor (that is, the formation of a mature 3′ terminus), the addition of polyadenylic acid, and the transport of messenger RNA from the nucleus to the cytoplasm. These 220 bases include a highly conserved sequence—AAUAAA (A, adenine; U, uracil). Four point mutations in this sequence—AACAAA, AAUUAA, AAUACA, and AAUGAA (C, cytosine; G, guanine)—prevent cleavage.