The sequence 5'-AAUAAA-3'forms parts of the recognition site for polyadenylation of late SV40 mRNAs.

We have observed three effects of deletion mutations on polyadenylation of late SV40 mRNAs. The first class of mutants lack segments (-3 to -14 bp) between the 5-AAUAAA-3' and normal poly(A) site. These mutants produce mRNas polyadenylated at new sites, downstream from the wild-type site. The poly(A) site is moved farther downstream as the deletions become larger; as a result, polyadenylation always occurs within an 11-19 nucleotide range from the AAUAAA sequence. The second class of mutants lack segments (-12 to -30 bp) between the AAUAAA sequence and the coding region of the mRNA. The poly(A) site for only one of these mutants was studied (dl1457, -12 bp). In this case, the spatial relationship between AAUAAA and poly(A) site is altered. dl1457 produces a class of mRNAs polyadenylated at the first Ca following the AAUAAA sequence, as well as other mRNAs polyadenylated farther downstream. Finally, a 16 bp deletion that includes the AAUAAA sequence prevents poly(A) addition.