Genetic evidence for a functional interaction between Saccharomyces cerevisiae CDC24 and CDC42

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Abstract
Cdc24p and Cdc42p are involved in the control of cell polarity during the Saccharomyces cerevisiae cell cycle. Cdc42p is a member of the Ras superfamily of GTPases and Cdc24p displays limited amino‐acid sequence similarity with the Dbl proto‐oncoprotein, which acts to stimulate guanine‐nucleotide exchange on human Cdc42p. We have performed several genetic experiments to test whether Cdc24p and Cdc42p interact within the cell. First, overexpression of Cdc24p suppressed the dominant‐negative cdc42D118A allele. Second, overexpression of wild‐type CDC24 and CDC42 genes together was a lethal event resulting in a morphological phenotype of large, round, unbudded cells, indicating a loss of cell polarity. Third, a cdc24ts cdc42ts double mutant exhibited a synthetic‐lethal phenotype at the semi‐permissive temperature of 30°C. These data suggest that Cdc24p and Cdc42p interact within the cell and that Cdc24p may be involved in the regulation of Cdc42p activity.