AFR1 promotes polarized apical morphogenesis in Saccharomyces cerevisiae

The G protein-coupled alpha-factor receptor promotes polarized growth toward a mating partner. alpha-Factor induces the expression of AFR1, which acts together with the receptor C terminus to promote normal morphogenesis. The function of AFR1 was investigated by engineering cells to constitutively express AFR1 without alpha-factor. Constitutive AFR1 expression caused cells to form elongated buds that demonstrate that AFR1 can also interact with the morphogenesis components that promote bud formation. A similar elongated bud phenotype is caused by mutation of the CDC3, CDC10, CDC11, and CDC12 genes, which encode putative filament proteins that form a ring at the bud neck. AFR1 may act directly on the filament proteins, since immunolocalization detected AFR1 at the bud neck and interaction of AFR1 and CDC12 was detected in the two-hybrid protein assay. AFR1 localized to the base of pheromone-induced projections. These results suggest that AFR1 and the putative filament proteins act together with the receptor to facilitate proper localization of components during mating.