Biochemical Characterization of the GTP-Binding Protein CDC42SC

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The long-term goal of this research is to understand the mechanisms that control cellular polarity during the eukaryotic cell cycle. The PI used the yeast Saccharomyces cerevisiae as a model system to study this process because it displays two different aspects of cellular polarity and is a relatively simple eukaryote that can be easily manipulated both physiologically and genetically using both classical and molecular genetic techniques (9). The goal of this research is to characterize the biochemical functions of the S.cerevisiae CDC42 (CDC42Sc) gene product, a putative GTP-binding protein. The PI will purify wild-type and mutant Cdc42Sc proteins and investigate (i) their capability to bind and hydrolyze GTP and (ii) their potential phosphorylation states. He will also isolate and characterize new proteins that interact with the Cdc42Sc protein. The existence of a human homolog of CDC42Sc, which he and others have shown to function in yeast (78,112) and to be an excellent in vitro phosphosubstrate for the epidermal growth factor (EGF) receptor tyrosine kinase (44), suggests that the molecular mechanisms involved in the control of cellular polarity could be conserved between yeasts and higher eukaryotes. Correlation of information obtained in S. cerevisiae to that from higher eukaryotes could provide valuable clues to the nature and function of low-molecular-weight GTP-binding proteins and to the intracellular signal-transduction mechanisms that control cellular polarity.