Stm1 Modulates mRNA Decay and Dhh1 Function in Saccharomyces cerevisiae

The control of mRNA degradation and translation are important for the regulation of gene expression. mRNA degradation is often initiated by deadenylation, which leads to decapping and 5'-3' decay. In the budding yeast Saccharomyces cerevisae, decapping is promoted by the Dhh1 and Pat1 proteins, which appear to both inhibit translation initiation and promote decapping. To understand the function of these factors, we identified the ribosome binding protein Sun I as a multicopy suppressor of the temperature sensitivity of the pat1 Delta strain. Stm1 loss-of-function alleles and overexpression strains show several genetic interactions with Pat1 and Dhh1 alleles in a manner consistent with Stm1 working Upstream of Dhh1 to promote Dhh1 function. Consistent with Stm1 affecting Dhh1 function, stm1 Delta strains are defective ill the degradation of the EDC1 and COX17mRNAs, whose decay is strongly affected by the loss of Dhh1. These results; identify Stm1 as an additional component of the mRNA degradation machinery and suggest a possible connection of mRNA decapping to ribosome function.