THE 5' UNTRANSLATED REGION OF THE PPR1 REGULATORY GENE DICTATES RAPID MESSENGER-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 that dictate mRNA decay rates in yeast, we have constructed PPR1/URA3 gene fusions and measured the half-lives of the resulting chimeric transcripts. The mRNA containing the URA3 coding region fused to the untranslated regions (UTR) of PPR1 decayed at a rate similar to the native PPR1 mRNA, suggesting that the instability of the PPR1 mRNA is not linked to its coding sequence. When the 5'-UTR of PPR1 was replaced by the 5'-UTR of URA3, the chimeric transcript was strongly stabilized, indicating 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 sufficient to destabilize the chimeric mRNA. We conclude that the PPR1 5'-UTR contains sequence(s) that can promote rapid mRNA decay in yeast.