THE 5' UNTRANSLATED REGION OF THE PPR1 REGULATORY GENE DICTATES RAPIDMESSENGER-RNA DECAY IN YEAST

In Saccharomyces cerevisiae, the mRNA encoded by the PPR1 gene is very unstable (t1/2 = 1 min), whereas the mRNA encoded by the URA3 gene is relatively stable (t1/2 = 10 min). To identify cis-acting sequences t hat dictate mRNA decay rates in yeast, we have constructed PPR1/URA3 g ene fusions and measured the half-lives of the resulting chimeric tran scripts. The mRNA containing the URA3 coding region fused to the untra nslated regions (UTR) of PPR1 decayed at a rate similar to the native PPR1 mRNA, suggesting that the instability of the PPR1 mRNA is not lin ked to its coding sequence. When the 5'-UTR of PPR1 was replaced by th e 5'-UTR of URA3, the chimeric transcript was strongly stabilized, ind icating that the 5'-UTR of PPR1 is required for the rapid decay of its mRNA. Fusion of this PPR1 5'-UTR to the URA3 coding region was suffic ient to destabilize the chimeric mRNA. We conclude that the PPR1 5'-UT R contains sequence(s) that can promote rapid mRNA decay in yeast.