THE ROLE OF CDC42 IN SIGNAL-TRANSDUCTION AND MATING OF THE BUDDING YEAST SACCHAROMYCES-CEREVISIAE

The small G-protein Cdc42 functions in many eukaryotic signal transduc tion pathways. In the budding yeast Saccharomyces cerevisiae, cells wi th defective Cdc42 fail to induce mating-specific genes in response to mating factor and to adopt the proper morphology for conjugation. Her e we show that the failure of mating factor-induced transcription is l argely the indirect result of arrest at a specific cell cycle position and/or the accumulation of high levels of the Cln1/2-Cdc28 kinase, a known repressor of mating factor signal transduction. Cdc42 defective cells with restored transcriptional induction have a partially restore d mating ability but are still defective in the morphological response to mating factor. These results show that Cdc42 is not required for t ransduction of the mating factor signal per se but that it is essentia l for proper mating factor-induced morphogenesis.