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 this 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 and solute environment (osmotic stress), and increasing ethanol toxicity and nutrient depletion as the fermentation proceeds. Understanding the mechanisms that enable yeast to cope with these stresses will allow us to develop fermentation strategies and yeast strains to enable more efficient fermentations. The conversion of fermentable sugars to ethanol is one of the prime objectives of the fermentation process. Yeast uses a family of 17 hexose transporters (Hxt1-17) to sense it sugar environment and to transport hexose sugars into the cell. The most important transporters during wine fermentations are Hxt1, Hxt3, Hxt5, Hxt6 and Hxt7. Hxt6 and Hxt7 are high affinity transporters that function toward the end of the fermentation when nutrients become limiting. We have shown that 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 produce ethanol. The Gid/Vid proteins form a complex, the Vid30c, which are responsible for the regulated internalization and degradation of the Hxt7 in response to changing nutrient conditions. However, the mechanism(s) of function of the Vid30c or its individual components are poorly understood. This proposal is aimed at increasing our understanding of the Vid30c in response to fermentation stresses.