CDC42: A Member of the ras Superfamily Involved in the Control of Cellular Polarity During the Saccharomyces cerevisiae Cell Cycle

GTP-binding proteins play vital roles in the control of a variety of cellular functions in both higher and lower eukaryotes, but the molecular mechanisms involved in this control have yet to be fully elucidated. ^{1 , 2} At least 15 GTP-binding proteins have been found to date in the yeast S. cerevisiae and their cellular functions are quite different, including the control of cellular morphogenesis (see below), ^{3 - 5} cell growth, ^{6 , 7} secretion and intraorganellar transport, ^{8 - 13} pheromone response, ¹⁴ and chromosome stability. ¹⁵ The evidence that functional overlap exists between some yeast and mammalian low molecular weight GTP-binding proteins, especially between CDC42Sc and its human homolog CDC42Hs/G25K (see below), suggests that common cellular roles for these gene products may exist in higher and lower eukaryotes. The understanding of cellular processes in yeast will, therefore, contribute to the understanding of normal and abnormal cellular processes in higher eukaryotic cells.