Different Domains of the Essential GTPase Cdc42p Required for Growth and Development of Saccharomyces cerevisiae

Abstract

In budding yeast, the Rho-type GTPase Cdc42p is essential for cell division and regulates pseudohyphal development and invasive growth. Here, we isolated 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 invasive growth. In haploid cells, Cdc42p is able to regulate invasive growth dependent on and independent of FLO11 gene expression. In diploid cells, Cdc42p regulates pseudohyphal development by controlling pseudohyphal cell (PH cell) morphogenesis and invasive growth. Several of the Cdc42p mutants isolated here block PH cell morphogenesis in response to nitrogen starvation without affecting morphology or polarity of yeast form cells in nutrient-rich conditions, indicating that these proteins are impaired for certain signaling functions. Interaction studies between development-specific Cdc42p mutants and known effector proteins indicate that in addition to the p21-activated (PAK)-like protein kinase Ste20p, the Cdc42p/Rac-interactive-binding domain containing Gic1p and Gic2p proteins and the PAK-like protein kinase Skm1p might be further effectors of Cdc42p that regulate pseudohyphal and invasive growth.

ACKNOWLEDGMENTS

We thank Maria Meyer for excellent technical assistance during the course of this work. We are grateful to Charles Boone, Roger Brent, J. Hegemann, D. Johnson, D. Lew, M. Peter, and S. Rupp for generously providing plasmids and strains. We thank Sven Krappmann and Naimeh Taheri for helpful comments on the manuscript.

This work was supported by grants from the Deutsche Forschungsgemeinschaft and the Volkswagenstiftung.