INVOLVEMENT OF YPT7P, A SMALL GTPASE, IN TRAFFIC FROM LATE ENDOSOME TO THE VACUOLE IN YEAST

The YPT7 gene encodes the Saccharomyces cerevisiae homolog of mammalia n rab7 protein. Data obtained from studies on a DELTAypt7 mutant sugge sted that Ypt7p is involved in the endocytic pathway in yeast (Wichman n et al., Cell 71, 1131-1142, 1992). We report here that endocytosed p heromone alpha-factor accumulates in late endosomes in DELTAypt7 cells , indicating that Ypt7p is involved in the regulation of transport ste ps from late endosomes to the vacuole. We also show that alpha-factor can be degraded in a PEP4-dependent manner in a prevacuolar/endosomal compartment in DELTAypt7 cells, providing independent evidence that th e pathways of vacuole biogenesis and endocytosis in yeast may intersec t in the endosomal membrane system.