ISOLATION OF DEGRADATION-DEFICIENT MUTANTS DEFECTIVE IN THE TARGETINGOF FRUCTOSE-1,6-BISPHOSPHATASE INTO THE VACUOLE FOR DEGRADATION IN SACCHAROMYCES-CEREVISIAE

The key regulatory enzyme in the gluconeogenesis pathway, fructose-l,6 -bisphosphatase (FBPase), is induced when Saccharomyces cerevisiae are grown in medium containing a poor carbon source. FBPase is targeted t o the yeast vacuole for degradation when glucose-starved cells are rep lenished with fresh glucose. To identify genes involved in the FBPase degradation pathway, mutants that failed to degrade FBPase in response to glucose were isolated using a colony-blotting procedure. These vac uolar import and degradation-deficient (vid) mutants were placed into 20 complementation groups. They are distinct from the known sec, vps o r pep mutants affecting protein secretion, vacuolar sorting and vacuol ar proteolysis in that they sort CpY correctly and regulate osmotic pr essure normally. Despite the presence of FBPase antigen in these mutan ts, FBPase is completely inactivated in all vid mutants, indicating th at the c-AMP-dependent signal transduction pathway and inactivation mu st function properly in vid mutants. vid mutants block FBPase degradat ion by accumulating FBPase in the cytosol and also in small vesicles i n the cytoplasm. FBPase may be targeted to small vesicles before uptak e by the vacuole.