PLASTICITY OF VACUOLE BIOGENESIS IN THE YEAST SACCHAROMYCES-CEREVISIAE

The genetic analysis of vacuole biogenesis and vacuolar protein sorting in the yeast Saccharomyces cerevisiae is briefly reviewed. Vacuolar biogenesis occurs by two routes, primarily via a branch from the default secretory pathway, but also by segregation of vacuolar material directly from the mother cell to the daughter bud. This is illustrated by strains carrying the ssv17-101 mutation. This causes a dramatic defect in the segregation of vacuolar material. The plasticity of vacuolar function is demonstrated. Mutations in ARO7 (SSV15) (chorismate mutase), GUT1 (glycerol kinase) and GUT2 (glycerol phosphate dehydrogenase), although all having a primary defect in intermediary metabolism, all cause the secretion of carboxypeptidase Y, a soluble vacuolar enzyme. In addition, an aro7-1 mutation also has a severe vacuolar morphology defect. This result establishes for the first time that defects in an enzyme in a biosynthetic pathway can have a pleiotropic defect in protein sorting.