Translation and a 42-nucleotide segment within the coding region of the mRNA encoded by the MATα1 gene are involved in promoting rapid mRNA decay in yeast

Abstract

In yeast, the mRNA encoded by the MATα1 gene is unstable (t1/2 = 5 min) and the mRNAs encoded by the ACT1 gene (t1/2 = 30 min) and the PGK1 gene (t1/2 = 45 min) are stable. To understand the RNA structural features that dictate mRNA decay rates in yeast, we have constructed PGK1/ MATα1 and ACT1/MATα1 gene fusions and analyzed the decay rates of the resultant chimeric transcripts. Fusion of a MATα1 segment containing 73% of the coding region and the 3′ untranslated region to either of the stable genes is sufficient to cause rapid decay of the chimeric mRNAs (t1/2 = 6-7.5 min). Sequences required for this rapid decay are not found in the MATα1 3′ untranslated region but are located within a 42-nucleotide segment of the coding region that has a high content (8 out of 14) of rare codons. Introduction of a translational stop codon upstream of this region stabilizes the hybrid mRNAs, indicating that the rapid decay promoted by these sequences is dependent on ribosomal translocation.