Complementing yeast rho1 mutation groups with distinct functional defects

Saccharomyces cerevisiae is a multifunctional molecular switch involved in establishment of cell morphogenesis. We systematically characterized isolat ed temperature-sensitive mutations in the RHO1 gene and identified two grou ps of rho1 mutations (rho1A and rho1B) possessing distinct functional defec ts. Biochemical and cytological analyses demonstrated that mutant cells of the rho1A and rho1B groups have defects in activation of the Rho1p effector s Pkc1p kinase and 1,3-beta -glucan synthase, respectively. Heteroallelic d iploid strains with rho1A and rho1B mutations were able to grow even at the restrictive temperature of the corresponding homoallelic diploid strains, showing intragenic complementation. The ability to activate both of the ess ential Rho1p effector proteins was restored in the heteroallelic diploid. T hus, each of the complementing rho1 mutation groups abolishes a distinct fu nction of Rho1p, activation of Pkc1p kinase or 1,3-beta -glucan synthase ac tivity.