Suppression of the Profilin-Deficient Phenotype by the RHO2 Signaling Pathway in Saccharomyces cerevisiae

Corresponding author: Dominick Pallotta, Pavillon Marchand, Laval University, Ste-Foy, Quebec G1K 7P4, Canada., pallotta{at}rsvs.ulaval.ca (E-mail)

Communicating editor: P. G. YOUNG

Profilin plays an important role in actin organization in all eukaryotic cells through mechanisms that are still poorly understood. We had previously shown that Mid2p, a transmembrane protein and a potential cell wall sensor, is an effective multicopy suppressor of the profilin-deficient phenotype in Saccharomyces cerevisiae. To better understand the role of Mid2p in the organization of the actin cytoskeleton, we isolated five additional multicopy suppressors of pfy1 cells that are Rom1p, Rom2p, Rho2p, Smy1p, and the previously uncharacterized protein Syp1p. The problems of caffeine and NaCl sensitivity, growth defects at 30° and 37°, the accumulation of intracellular vesicular structures, and a random budding pattern in pfy1 cells are corrected by all the suppressors tested. This is accompanied by a partial repolarization of the cortical actin patches without the formation of visible actin cables. The overexpression of Mid2p, Rom2p, and Syp1p, but not the overexpression of Rho2p and Smy1p, results in an abnormally thick cell wall in wild-type and pfy1 cells. Since none of the suppressors, except Rho2p, can correct the phenotype of the pfy1-111/rho2 strain, we propose a model in which the suppressors act through the Rho2p signaling pathway to repolarize cortical actin patches.

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