Abstract
RNA binding proteins (RBPs) are vital to the regulation of mRNA transcripts, and can alter mRNA localization, degradation, translation, and storage. Whi3 was originally identified in a screen for small cell size mutants, and has since been characterized as an RBP. The identification of Whi3-interacting mRNAs involved in mediating cellular responses to stress suggested that Whi3 might be involved in stress-responsive RNA processing. We show that Whi3 localizes to stress granules in response to glucose deprivation or heat shock. The kinetics and pattern of Whi3 localization in response to a range of temperatures were subtly but distinctly different from those of known components of RNA processing granules. Deletion of Whi3 resulted in an increase in the relative abundance of Whi3 target RNAs, either in the presence or absence of heat shock. Increased levels of the CLN3 mRNA in whi3Δ cells may explain their decreased cell size. Another mRNA target of Whi3 encodes the zinc-responsive transcription factor Zap1, suggesting a role for Whi3 in response to zinc stress. Indeed, we found that whi3Δ cells have enhanced sensitivity to zinc toxicity. Together our results suggest an expanded model for Whi3 function: in addition to its role as a regulator of the cell cycle, Whi3 may have a role in stress-dependent RNA processing and responses to a variety of stress conditions.
Highlights
The budding yeast Saccharomyces cerevisiae adapts to cellular stress by arresting the cell cycle and altering a variety of RNA metabolic processes
To investigate the molecular function of Whi3, we examined its localization using a fully functional WHI3-GFP fusion gene, integrated at the WHI3 locus to maintain endogenous regulation of its expression
Because Whi3 shares characteristics with proteins that localize to stress granules, and is reported to interact with Pub1, a known component of stress granules [18], we examined Whi3-GFP localization in cells deprived of glucose, a condition that induces stress-granule formation in yeast [5,20,21,22,23,24]
Summary
The budding yeast Saccharomyces cerevisiae adapts to cellular stress by arresting the cell cycle and altering a variety of RNA metabolic processes. Though P-bodies and stress granules share overlapping functions and protein components, stress granules only appear during periods of cellular stress and contain a wider array of RNA processing proteins than P-bodies, such as translation initiation factors, 40 S ribosomal subunits, and stability-promoting RNA binding proteins [5,6,7]. This broad repertoire of RNA processing proteins allows stress granules to tailor stress responses by promoting storage or translation of particular mRNAs, while other mRNAs undergo decay [3,6]
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