Analysis of chimeric mRNAs derived from theSTE3mRNA identifies multiple regions within yeast mRNAs that modulate mRNA decay

Abstract

In the yeast Saccharomyces cerevisiae unstable mRNAs decay 10-20 fold more rapidly than stable mRNAs. In order to examine the basis for the differences in decay rate of the unstable STE3 mRNA and the stable PGK1 and ACT1 mRNAs we have constructed and measured the decay rates of numerous chimeric mRNAs. These experiments indicate that multiple regions within yeast mRNAs are involved in modulating mRNA decay rates. Our results suggest that at least two regions within the STE3 mRNA are involved in stimulating rapid decay. One region is located within the coding region and requires sequences between codons 13 and 179. In addition, the STE3 3' UT can also function to stimulate decay. Surprisingly, the STE3 3' UT is not sufficient to accelerate the turnover of the stable PGK1 transcript unless portions of the PGK1 coding region are first deleted. These results not only identify sequences that function within yeast to stimulate mRNA turnover but also have important implications for an understanding of the basis of differences in eukaryotic mRNA decay rates.

A small segment of the MAT alpha 1 transcript promotes mRNA decay in Saccharomyces cerevisiae: a stimulatory role for rare codons.

“…Our data are in contrast to those of a previous report which concluded that the replacement of the first 164 codons of the PGKI mRNA with all rare codons was sufficient to destabilize this transcript (20). However, since these codon changes made numerous alterations in the primary sequence of the PGKI coding sequence within a region that has been implicated in transcriptional activation (24) and/or mRNA stability (16) and no measurements of mRNA decay rate or transcription rate were performed, this prior conclusion must be treated with extreme caution.…”

“…Our results defining the MIE are consistent with the general view that specific sequences within mRNAs control their halflives (9). However, several of our results reported here and elsewhere (16,25) suggest that the observed decay rates of different mRNAs may depend on the combined effects of multiple elements within each mRNA. For example, although the MIE can increase the rate of decay of the PGKI transcript by fivefold, this chimeric transcript is still approximately two-to threefold more stable than the parental MATod mRNA.…”

“…pRP22 was created by inserting a 144-nucleotide EcoRI fragment containing a portion of the GALl UAS from nucleotides 365 to 509 (a kind gift from Mark Johnston) into EcoRI-cut pRP10 (16). Plasmid pRIPlH.Potl (27) was linearized by digestion with PvuI, and overhanging ends were filled.…”

“…Recent experiments, examining the decay rates of chimeric and/or mutant transcripts, suggest that at least in some cases, there are discrete sequence elements that affect mRNA turnover rates (for reviews, see references 19 and 28). These instability elements have been described in the protein coding and/or 3' untranslated regions of a small number of mRNAs.Determinants of mRNA stability have been identified in the protein coding regions of mammalian (14,32,41) and yeast (16,17,27,36) transcripts. These observations suggest that the coding region will be a common location for sequences that affect mRNA half-lives (t1j2s).…”

“…Determinants of mRNA stability have been identified in the protein coding regions of mammalian (14,32,41) and yeast (16,17,27,36) transcripts. These observations suggest that the coding region will be a common location for se-quences that affect mRNA half-lives (t1j2s).…”