An important aspect of cell regulation is the controlled delivery of transport proteins to the plasma membrane, allowing the cells capacity to take up small molecules to respond to extracellular signals. Dr. Kaiser's research group proposes a combination of genetic and biochemical experiments in the yeast S. cerevisiae to give fundamental insight into the mechanism of regulated delivery of integral membrane proteins to the plasma membrane. Recent work in Dr. Kaiser's laboratory has shown that in yeast delivery of the general amino acid permease (Gap1) to the plasma membrane responds to the nitrogen source in the growth medium. The regulation of the cellular location of Gap1 takes place in the trans-Golgi where Gap1 is loaded into transport vesicles directed either to the plasma membrane or to the vacuole. In this application, Dr. Kaiser proposes to elucidate the mechanism of Gap1 sorting in the trans-Golgi. These studies will include development of in vivo and in vitro assays for the formation of Gap1-containing vesicles, and the identification and characterization of gene products that control Gap1p sorting. The regulated delivery of proteins to the plasma membrane is key to human cell physiology. For example, the GLUT4 glucose transporter is delivered to the plasma membrane of fat and muscle cells in response to insulin, and defects in this regulated trafficking are though to be a root cause of non-insulin- dependent diabetes. Little is known of the mechanisms that control the location of GLUT4 or other regulated membrane proteins in humans. However, in S. cerevisiae it will be possible to apply the full power of a well developed genetic organism to uncover the genes and proteins responsible for regulated sorting in the Golgi. The genes from S. cerevisiae should give access to the mammalian genes that perform similar functions, opening the way to new methods for the diagnosis of dysfunctional sorting in mammalian cells and providing new opportunities to selectively alter the plasma membrane composition of cells.
