EVIDENCE FOR PHYSICAL AND FUNCTIONAL INTERACTIONS AMONG 2 SACCHAROMYCES-CEREVISIAE SH3 DOMAIN PROTEINS, AN ADENYLYL CYCLASE-ASSOCIATED PROTEIN AND THE ACTIN CYTOSKELETON

n a variety of organisms, a number of proteins associated with the cor tical actin cytoskeleton contain SH3 domains, suggesting that these do mains may provide the physical basis for functional interactions among structural and regulatory proteins in the actin cytoskeleton. We pres ent evidence that SH3 domains mediate at least two independent functio ns of the Saccharomyces cerevisiae actin-binding protein Abp1p in vivo . Abp1p contains a single SH3 domain that has recently been shown to b ind in vitro to the adenylyl cyclase-associated protein Srv2p. Immunof luorescence analysis of Srv2p subcellular localization in strains carr ying mutations in either ABP1 or SRV2 reveals that the Abp1p SH3 domai n mediates the normal association of Srv2p with the cortical actin cyt oskeleton. We also show that a site in Abp1p itself is specifically bo und by the SH3 domain of the actin-associated protein Rvs167p. Genetic analysis provides evidence that Abp1p and Rvs167p have functions that are closely interrelated. Abp1 null mutations, like rvs167 mutations, result in defects in sporulation and reduced viability under certain suboptimal growth conditions. In addition, mutations in ABP1 and RVS16 7 yield similar profiles of genetic ''synthetic lethal'' interactions when combined with mutations in genes encoding other cytoskeletal comp onents. Mutations which specifically disrupt the SH3 domain-mediated i nteraction between Abp1p and Srv2p, however, show none of the shared p henotypes of abp1 and rvs167 mutations. We conclude that the Abp1p SH3 domain mediates the association of Srv2p with the cortical actin cyto skeleton, and that Abp1p performs a distinct function that is likely t o involve binding by the Rvs167p SH3 domain. Overall, work presented h ere illustrates how SH3 domains can integrate the activities of multip le actin cytoskeleton proteins in response to varying environmental co nditions.