Evidence for the genetic interaction between the actin-binding protein Vrp1 and the RhoGAP Rgd1 mediated through Rho3p and Rho4p in Saccharomyces cerevisiae

The non-essential RGD1 gene from Saccharomyces cerevisiae encodes a protein that has been characterized in vitro as a Rho GTPase activating protein (R hoGAP) for the Rho3 and Rho4 proteins. Rgd1p, which displays a conserved FC H-coiled coil-RhoGAP domain organization, showed a patch-like distribution in the cell, including a localization in growing buds. Using a genetic scre en, we found that rgd1 Delta and vrp1 Delta mutations exhibited a synthetic lethality, thus revealing an interaction between these genes. The VRP1 pro duct is an actin and myosin interacting protein involved in polarized growt h. Using mutant forms of both Rho3 and Rho4 proteins, we provide evidence f or the involvement of these two GTPases in RGD1-VRP1 co-lethality. In addit ion, these results strongly argue in favour of Rho3p and Rho4p being the ta rgets of Rgd1p RhoGAP activity in vivo. Genetic relationships between eithe r VRP1 or RGD1 and actin cytoskeleton-linked genes were also studied. These and other well-established data support the idea that Vrp1, Las17, Rvs167 proteins belong to the same complex. This protein structure might act with myosins in various actin cytoskeleton-based activities, in co-operation wit h a Rho3p/Rho4p signalling pathway that is negatively regulated by Rgd1p GA P activity.