Elucidating the biological role and regulation of conserved actin cytoskeleton proteins in the budding yeast Saccharomyces cerevisiae

The function of the actin cytoskeleton in the budding yeast, Saccharomyces cerevisiae depends on the ability of a network of actin filaments and other proteins to change dynamically in response to intra and extra-cellular cues. Actin-binding proteins and regulatory proteins interact and function together to regulate the assembly and disassembly of the actin filaments. The specific activity and biological function of many of these actin-associated proteins remains unclear. In this doctoral work, I have sought to uncover the biological role and regulation of several conserved actin cytoskeleton proteins: coronin (Crn1), the Arp2/3 complex and the yeast amphiphysins (Rvs161 and Rvs167). I report on a novel mode of Arp2/3 complex regulation mediated by the highly conserved actin binding protein coronin. I show that yeast coronin (Crn1) physically associates with the Arp2/3 complex and inhibits WA- and Abp1-activated actin nucleation in vitro. I also report on a possible role for phosphorylation in regulating the activity of Crn1 in vivo. I show evidence that Crn1 is a substrate for Pcl-Pho85 in vitro and that Pho85 regulates the interaction between Cm1 and the Arp2/3 complex in vivo. I also present genetic and biochemical evidence that the yeast amphiphysin proteins, Rvs161 and Rvs167, function together during vegetative growth and during mating. In addition, I have identified an essential role for the SH3 domain of Rvs167 in the absence of the actin cytoskeleton proteins Sla1 and End3. My work identifies novel roles for Crn1 as a regulator of Arp2/3-dependent actin nucleation, provides evidence that the activity of Crn1 may be regulated by phosphorylation and shows evidence for a role for the Rvs161--167 complex in a variety of cellular processes, including mating.