The control of translation and mRNA degradation plays a key role in the regulation of eukaryotic gene expression. In the cytosol, mRNAs engaged in translation are distributed throughout the cytosol, while translationally inactive mRNAs can accumulate in P bodies, in complex with mRNA degradation and translation repression machinery, or in stress granules, which appear to be mRNAs stalled in translation initiation. Here we discuss how these different granules suggest a dynamic model for the metabolism of cytoplasmic mRNAs wherein they cycle between different mRNP states with different functional properties and subcellular locations.

The control of translation is a critical aspect of gene regulation. It is often inversely related to mRNA degradation and is typically controlled during initiation. The Stm1 protein in Saccharomyces cerevisiae has been shown to interact with ribosomes, affect the interaction of eEF3 with ribosomes, and promote the decapping of a subclass of mRNAs. We demonstrate that in vitro Stm1 inhibits translation after formation of an 80S complex. This suggests that Stm1 modulates translation and mRNA decapping by controlling translation elongation.

Messenger RNA degradation is an important point of control for gene expression. Genomewide studies on mRNA stability have demonstrated its importance in adaptation and stress response. Most of the key players in mRNA decay appear to have been identified. The study of these proteins brings insight into the mechanism of general and specific targeting of transcripts for degradation. Recruitment and assembly of mRNP complexes enhance and bring specificity to mRNA decay. mRNP complexes can form larger structures that have been found to be ubiquitous in nature. Discovery of P-Bodies, an archetype of these sort of aggregates, has generated interest in the question of where mRNA degrades. This is currently an open question under extensive investigation. This review will discuss in detail the recent developments in the regulation of mRNA decay focusing on yeast as a model system.

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 59-39 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 Stm1 as a multicopy suppressor of the temperature sensitivity of the pat1D 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, stm1D strains are defective in the degradation of the EDC1 and COX17 mRNAs, 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.