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Vol. 17, Issue 6, 2824-2838, June 2006

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Cdc42p GDP/GTP Cycling Is Necessary for Efficient Cell Fusion during Yeast Mating

Sophie Barale^*,, Derek McCusker^,, and Robert A. Arkowitz^*

*Institute of Signaling, Developmental Biology, and Cancer, Centre National de la Recherche Scientifique UMR 6543, Université de Nice, Faculté des Sciences-Parc Valrose, 06108 Nice Cedex 2, France; and Department of Biology, Sinsheimer Laboratories, University of California at Santa Cruz, Santa Cruz, CA 95064

Submitted November 14, 2005; Revised March 2, 2006; Accepted March 20, 2006
Monitoring Editor: Janet Shaw

The highly conserved small Rho G-protein, Cdc42p plays a critical role in cell polarity and cytoskeleton organization in all eukaryotes. In the yeast Saccharomyces cerevisiae, Cdc42p is important for cell polarity establishment, septin ring assembly, and pheromone-dependent MAP-kinase signaling during the yeast mating process. In this study, we further investigated the role of Cdc42p in the mating process by screening for specific mating defective cdc42 alleles. We have identified and characterized novel mating defective cdc42 alleles that are unaffected in vegetative cell polarity. Replacement of the Cdc42p Val36 residue with Met resulted in a specific cell fusion defect. This cdc42[V36M] mutant responded to mating pheromone but was defective in cell fusion and in localization of the cell fusion protein Fus1p, similar to a previously isolated cdc24 (cdc24-m6) mutant. Overexpression of a fast cycling Cdc42p mutant suppressed the cdc24-m6 fusion defect and conversely, overexpression of Cdc24p suppressed the cdc42[V36M] fusion defect. Taken together, our results indicate that Cdc42p GDP–GTP cycling is critical for efficient cell fusion.

These authors contributed equally to this work.

Address correspondence to: Robert A. Arkowitz ( arkowitz{at}unice.fr)

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