Maltose fermentation in Saccharomyces is initiated by its active transport into the cell by maltose permease. The level of activity of maltose permease is under dual regulation. Firstly, transcription of the gene encoding maltose permease is maltose-induced and glucose-repressed. Secondly, maltose permease is glucose-inactivated, that is, the ability to transport maltose is rapidly lost following the addition of glucose to an induced culture. This research will determine the mechanism of glucose-induced inactivation of maltose permease. The MAL61 gene which encodes maltose permease at the MAL6 locus has been sequenced. Antibody to maltose permease will be isolated and used to follow the fate of the maltose permease protein during glucose-induced inactivation. Antibody will be raised to fusion products or to peptides. The kinetics of maltose transport and of glucose-induced inactivation of maltose permease will be determined in genetically defined strains. The possibility that maltose permease is modified, selectively removed from the plasma membrane or proteolytically degraded during the inactivation process will be explored. Also, glucose inactivation resistant mutations in MAL61 using in vitro mutagenesis techniques will be isolated. In the regulation of cellular growth and metabolism, cells are often responding to changes in the extra-cellular environment and this response is mediated by integral membrane proteins. Glucose-induced inactivation of maltose permease is an example of such a regulatory system. The cell is responding to changes in the extra-cellular levels of glucose but the "glucose receptor" remains undefined and the intracellular response is poorly understood. This research will provide insight into these processes. It will also provide an opportunity to study protein turnover and subcellular localization as mechanisms of regulation. These regulatory mechanisms are important and poorly understood processes involved in memory, aging and differentiation.
