GENETIC INTERACTION WITH VPS8-200 ALLOWS PARTIAL SUPPRESSION OF THE VESTIGIAL VACUOLE PHENOTYPE CAUSED BY A PEP5 MUTATION IN SACCHAROMYCES-CEREVISIAE

pep5 mutants of Saccharomyces cerevisiae accumulate inactive precursor s to the vacuolar hydrolases. In addition, they show a vestigial vacuo le morphology and a sensitivity to growth on media containing excess d ivalent cations. This pleiotropic phenotype observed for pep5::TRP1 mu tants is partially suppressed by the vps8-200 allele. pep5::TRP1 vps8- 200 mutants show near wild-type levels of mature-sized soluble vacuola r hydrolases, growth on zinc-containing medium, and a more ''wild-type '' vacuolar morphology; however, aminopeptidase I and alkaline phospha tase accumulate as precursors. These data suggest that Pep5p is a bifu nctional protein and that the TRP1 insertion does not eliminate functi on, but results in a shorter peptide that call interact with Vps8-200p , allowing for partial function. vps8 deletion/disruption mutants cont ain a single enlarged vacuole. This genetic interaction was unexpected , since Pep5p was thought to interact more directly with the vacuole, and Vps8p is thought to play a role in transport between the Golgi com plex and the prevacuolar compartment. The data are consistent with Pep 5p functioning both at the site of Vps8p function and more closely pro ximal to tile vacuole. They also provide evidence that the three trans port pathways to the vacuole either converge or share gene products at late step(s) in the pathway(s).