Specific pre-cleavage and post-cleavage complexes involved in the formation of SV40 late mRNA 3' termini in vitro.

Complexes form between processing factors present in a crude nuclear extract from HeLa cells and a simian virus 40 (SV40) late pre-mRNA which spans the polyadenylation [poly(A)] site. A specific 'pre-cleavage complex' forms on the pre-mRNA before cleavage. Formation of this complex requires the highly conserved sequence AAUAAA: it is prevented by mutations in AAUAAA, and by annealing DNA oligonucleotides to that sequence. After cleavage, the 5' half-molecule is found in a distinct 'post-cleavage complex'. In contrast, the 3' half-molecule is released. After cleavage and polyadenylation, polyadenylated RNA also is released. De novo formation of the post-cleavage complex requires AAUAAA and a nearby 3' terminus. Competition experiments suggest that a component which recognizes AAUAAA is required for formation of both pre- and post-cleavage complexes.