FLEXIBILITY AND INTERCHANGEABILITY OF POLYADENYLATION SIGNALS IN SACCHAROMYCES-CEREVISIAE

Various signal motifs have been reported to be essential for proper mR NA 3'-end formation in the yeast Saccharomyces cerevisiae. However, no ne of these motifs has been shown to be sufficient to direct 3'-end pr ocessing and/or transcription termination. Therefore, several structur al motifs have to act in concert for efficient 3'-end formation. In th e region upstream of the three polyadenylation sites of the yeast gene for alcohol dehydrogenase I (ADH1), we have identified a hitherto unk nown signal sequence contained within the octamer AAAAAAAA. This motif , located 11 nucleotides upstream of the first ADH1 polyadenylation si te, is responsible for the utilization of this site in vitro and in vi vo, since mutational alteration drastically reduced 3'-end formation a t this position. Insertion of 38 ADH1-derived nucleotides encompassing the (A), motif into the 3'-end formation deficient cyc1-512 deletion mutant restored full processing capacity in vitro. Insertion of the oc tamer alone did not restore 3'-end formation, although mutation of the (A), motif in the functional construct had abolished 3'-end processin g activity almost completely. This demonstrates that the sequence AAAA AAAA is a necessary, although not sufficient, signal for efficient mRN A 3'-end formation in S. cerevisiae.