Grant: Discovery Grants Program - Individual

The yeast Saccharomyces cerevisiae have two very important functions: it serves as an eukaryotic model organism in which fundamental processes of eukaryotic cell biology, molecular biology and metabolism can be studied, and it has enormous industrial relevance as it serves to produce bread, wine, beer and bio-ethanol. During beverage and bio-ethanol production the yeast is used to ferment high concentrations of fermentable sugars into ethanol and carbon dioxide. These production processes present the yeast with a variety of stresses that ultimately influences its ability to perform fermentations efficiently. Fermentation stresses include an initial high sugar content (osmotic stress), and increasing ethanol production and nutrietn (carbon and nitrogen) depletion as the fermentation proceeds. Understanding the mechanisms that enable yeast to cope with these stresses will allow us to develop yeast strains that are more efficient during the fermentation process. Effective fermentations are largely determined by the yeast's ability to take up and ferment glucose and fructose. A family of hexose transporters (Hxt1-17) that range in their affinities for glucose or fructose are used by the yeast to take up fermentable carbon sources and its tolerance to ethanol. The most important transporters during wine (batch) fermentations have are Hxt1, Hxt3, Hxt5, Hxt6 and Hxt7.We have shown that a family of yeast genes, the GID/VID genes, are needed by the yeast to respond effectively to nutrient depletion, osmotic stress and, surprisingly, influence the yeast's ability to take up glucose and to produce ethanol. The Gid/Vid proteins form a complex, the Gid Protein Complex (GPC), which are responsible for the regulated proteolysis of FBPase when carbon-starved cells are replenished with glucose. We have shown that components of the GPC are needed for the regulated degradation of Hxt7 in response to changing nutrient conditions.  However, the mechanism(s) of function of the GPC or its individual components, are poorly understood. This proposal is aimed at increasing our understanding of the GPC and, specifically, four of its components.