Requirement of A-A-U-A-A-A and adjacent downstream sequences for SV40 early polyadenylation

RNA mapping experiments and chloramphenicol acetyltransferase assays were used to analyze polyadenylation in COS cells of transcripts from derivatives of pSV2-neo and pSV2-cat, in which the SV40 early poly(A) signal has been modified. Neither the sequence A-A-U-A-A-A nor the sequences located immediately downstream from it in the SV40 early gene appear to function by themselves as a poly(A) signal. When combined, however, these two elements form a poly(A) signal whose efficiency and specificity closely resemble those of the wild type signal. The addition of six nucleotides between the A-A-U-A-A-A sequence and the poly(A) site has no detectable effect on the efficiency or site of polyadenylation. Deletion of the 60 nucleotides immediately upstream from the hexanucleotide also has no detectable effect on polyadenylation. Therefore, A-A-U-A-A-A and sequences downstream from it appear to be sufficient for SV40 early polyadenylation.