Suppression of the profilin-deficient phenotype by the RHO2 signaling pathway in Saccharomyces cerevisiae

Profilin plays an important role in actin organization in all eukaryotic ce lls 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 i n Saccharomyces cerevisiae. To better understand the role of Mid2p in the o rganization of the actin cytoskeleton, we isolated five additional multicop y suppressors of pfy1 Delta cells that are Rom1p, Rom2p, Rho2p, Smy1p, and the previously uncharacterized protein Syp1p. The problems of caffeine and NaCl sensitivity, growth defects at 30 degrees and 37 degrees, the accumula tion of intracellular vesicular structures, and a random budding pattern in pfy1 Delta cells are corrected by all the suppressors tested. This is acco mpanied by a partial repolarization of the cortical actin patches without t he formation of visible actin cables. The overexpression of Mid2p, Rom2p, a nd Syp1p, but not the overexpression of Rho2p and Smy1p, results in an abno rmally thick cell wall in wild-type and pfy1 Delta cells. Since none of the suppressors, except Rho2p, can correct the phenotype of the pfy1-111/rho2 Delta strain, we propose a model in which the suppressors act through the R ho2p signaling pathway to repolarize cortical actin patches.