Different domains of the essential GTPase cdc42p required for growth and development of Saccharomyces cerevisiae

In budding yeast, the Rho-type GTPase Cdc42p is essential for cell division and regulates pseudohyphal development and invasive growth. Here, we isola ted novel Cdc42p mutant proteins with single-amino-acid substitutions that are sufficient to uncouple functions of Cdc42p essential for cell division from regulatory functions required for pseudohyphal development and invasiv e growth. In haploid cells, Cdc42p is able to regulate invasive growth depe ndent on and independent of FLO11 gene expression. In diploid cells, Cdc42p regulates pseudohyphal development by controlling pseudohyphal cell (PH ce ll) morphogenesis and invasive growth. Several of the Cdc42p mutants isolat ed here block PH cell morphogenesis in response to nitrogen starvation with out affecting morphology or polarity of yeast form cells in nutrient-rich c onditions, indicating that these proteins are impaired for certain signalin g functions. Interaction studies between development-specific Cdc42p mutant s and known effector proteins indicate that in addition to the p21-activate d (PAK)-like protein kinase Ste20p, the Cdc42p/Rac-interactive-binding doma in containing Gic1p and Gic2p proteins and the PAK-like protein kinase Skm1 p might be further effecters Of Cdc42p that regulate pseudohyphal and invas ive growth.