| Abstract: | The poly(A) site of bovine prolactin (bPRL) mRNA was examined by phased priming of cDNA synthesis with oligodeoxynucleotides of the general sequence d(pT8-N-N'). The existence of multiple poly(A)-adjacent sequences in bPRL mRNA was indicated by the production of specific chain-termination fragments with at least three d(pT8-N-N') sequences. Comparison of the sequence bands produced by initiation of cDNA synthesis on the bPRL mRNA template with d(pT8-A-G), d(pT8-G-A), and d(pT8-C-G) revealed a shifted pattern of identical fragments. The shift in position of related sequence bands on the gel suggested that the difference in length of the three major bPRL mRNA species occurred within a span of 12 nucleotides. Sequence analysis conducted with the three d(pT8-N-N') primers gave identical nucleotide sequences for the 3' noncoding region of the bPRL mRNA species and suggested that the mRNA molecules were heterogeneous in length. The existence of multiple poly(A) sites was confirmed by determination of the nucleotide sequence of bPRL cDNA clones containing two of the major poly(A)-adjacent sequences predicted by the oligodeoxynucleotide primers. The mRNA molecules containing these multiple poly(A)-addition sites were shown to be present in the bPRL mRNA obtained from a single pituitary gland. The variation in the poly(A) junction of bPRL mRNA may be a reflection of the processing events at the 3' terminus of mRNAs. |
