Posttranscriptional Regulation of Flocculation in Fission Yeast

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Flocculation is an inherent property of yeasts that involves the aggregation of individual cells into clumps called flocs. The flocculent phenotype is very important in the yeast industry as it allows for an efficient and cost-effective method of cell removal from the biotechnological product. Related cell surface proteins to those involved in flocculation are also implicated in invasive growth and biofilm formation which contribute to the virulence and antifungal resistance of pathogenic yeasts. Therefore, the significant impact of yeast flocculation in these areas highlights the importance of fully comprehending how this process is regulated. A disproportionate effort has focused mainly on transcriptional (mRNA synthesis) rather than posttranscriptional (mRNA stability and translation) control of yeast flocculation. The genetic control of flocculation in any yeast model system at the posttranscriptional level is not well understood. We have recently discovered a Pumilio protein with a flocculation role in the fission yeast Schizosaccharomces pombe. The Pumilio (Puf) protein family posttranscriptionally regulate gene expression by interacting directly with a subset of mRNA targets to induce their turnover, repress their translation and affect cellular localization. Our goal is to apply a powerful combination of genetics, cell biology, biochemistry and functional genomics in the fission yeast model system to elucidate Pumilio protein function in flocculation. The specific objectives of this research proposal are to determine the mRNA targets, mode of posttranscriptional control and protein partners of this Pumilio protein. We will also screen a collection of approximately 3000 deletion mutant strains for defects in flocculation to identify novel genes that control this process. Our view is that this research will lead to novel mechanistic insights in the posttranscriptional regulation of genes in yeast flocculation. The knowledge generated would be useful to the yeast industry and potentially identify new drug targets for pathogenic yeasts. Furthermore, this research will also have the potential to reveal general themes or rules of posttranscriptional control across all eukaryotes.