Signals sufficient for 3'-end formation of yeast mRNA.

The following three elements were previously shown to be required for 3'-end formation of mRNA in the yeast Saccharomyces cerevisiae: (i) the efficiency element TATATA or related sequences, which function by enhancing the efficiency of downstream positioning elements; (ii) the positioning element AATAAA or related sequences, which position the poly(A) site; and (iii) the actual poly(A) site, which is usually Py(A)n. In this study, we synthesized a 39-pb poly(A) signal that contained the optimum sequences of these three elements. By inserting the synthetic 3'-end-forming signal into various positions of a CYC1-lacZ fusion gene, we showed that truncated transcripts of the expected sizes were generated. Furthermore, the poly(A) sites of the truncated transcripts were mapped to the expected poly(A) site within the synthetic signal. Our findings establish that the three elements are not only necessary but also sufficient for mRNA 3'-end formation in S. cerevisiae.