SH3 domain-containing proteins and the actin cytoskeleton in yeast.

SH3 (Src homology-3) domains are involved in protein-protein interactions through proline-rich domains. Many SH3-containing proteins are implicated in actin cytoskeleton organization. The aim of our ongoing work is to study the functions of the SH3-containing proteins in actin cytoskeleton regulation. The yeast Saccharomyces cerevisiae proteome includes 29 SH3 domains distributed in 25 proteins. We have examined the direct involvement of these SH3 domains in actin polymerization using an in vitro polymerization assay on GST (glutathione S-transferase)-SH3-coated beads. As expected, not all SH3 domains show polymerization activity, and many recruit distinct partners as assessed by microscopy and pull-down experiments. One such partner, Las17p, the yeast homologue of WASP (Wiskott-Aldrich syndrome protein), was assayed because it stimulates actin nucleation via the Arp2/3 (actin-related protein 2/3) complex. Ultimately, proteins involved in specific biological processes, such as membrane trafficking, may also be recruited by some of these SH3 domains, shedding light on the SH3-containing proteins and actin cytoskeleton functions in these processes.