USE OF A SYNTHETIC LETHAL SCREEN TO IDENTIFY YEAST MUTANTS IMPAIRED IN ENDOCYTOSIS, VACUOLAR PROTEIN SORTING AND THE ORGANIZATION OF THE CYTOSKELETON

To identify new genes whose products act on the endocytic and vacuolar protein sorting pathways, we screened for mutants that display synthe tic growth defects with Delta ypt51, a mutant impaired in membrane tra ffic at a point where these pathways intersect. Seven mutants that fel l into six different complementation groups were found to fit this cri terium. Two of the mutants (ysl1 and ysl2) are new, two others are def ective in the VAN1 gene. Mutants in VAN1 were previously identified by their resistance to the drug orthovanadate. The others represent know n endocytosis (rvs167 and sac6) and vacuolar protein sorting (vps41) m utants. As suggested by their genetic interactions with Delta ypt51 th e newly identified mutants are impaired in endocytosis, vacuolar prote in sorting and vacuole biogenesis. In addition, van1 and ysl2 display actin cytoskeletal defects.