VID24P, A NOVEL PROTEIN LOCALIZED TO THE FRUCTOSE-1,6-BISPHOSPHATASE-CONTAINING VESICLES, REGULATES TARGETING OF FRUCTOSE-1,6-BISPHOSPHATASE FROM THE VESICLES TO THE VACUOLE FOR DEGRADATION

Glucose regulates the degradation of the key gluconeogenic enzyme, fru ctose-1,6-bisphosphatase (FBPase), in Saccharomyces cerevisiae. FBPase is targeted from the cytosol to a novel type of vesicle, and then to the vacuole for degradation when yeast cells are transferred from medi um containing poor carbon sources to fresh glucose. To identify protei ns involved in the FBPase degradation pathway, we cloned our first VID (vacuolar import and degradation) gene. The VID24 gene was identified by complementation of the FBPase degradation defect of the vid24-1 mu tant. Vid24p is a novel protein of 41 kD and is synthesized in respons e to glucose. Vid24p is localized to the FBPase-containing vesicles as a peripheral membrane protein. In the absence of functional Vid24p, F BPase accumulates in the vesicles and fails to move to the vacuole, su ggesting that Vid24p regulates FBPase targeting from the vesicles to t he vacuole. FBPase sequestration into the vesicles is not affected in the vid24-1 mutant, indicating that Vid24p acts after FBPase sequestra tion into the vesicles has occurred. Vid24p is the first protein ident ified that marks the FBPase-containing vesicles and plays a critical r ole in delivering FBPase from the vesicles to the vacuole for degradat ion.