THE CYTOPLASMIC TAIL DOMAIN OF THE VACUOLAR PROTEIN SORTING RECEPTOR VPS1OP AND A SUBSET OF VPS GENE-PRODUCTS REGULATE RECEPTOR STABILITY, FUNCTION, AND LOCALIZATION

VPS10 of Saccharomyces cerevisiae encodes a type I transmembrane recep tor protein required for the sorting of the soluble vacuolar hydrolase carboxypeptidase Y (CPY). To characterize the essential structural fe atures and intercompartmental transport itinerary of the CPY receptor, we have constructed mutant forms of Vps10p that alter the carboxyterm inal cytoplasmic tail of the protein. In addition, we have analyzed th e effect these mutations as well as mutations in several VPS genes hav e on the function, stability, and localization of Vps10p. Although wil d-type Vps10p is very stable over a 3-h chase period, overproduction o f Vps10p results in PEP4-dependent degradation of the receptor. Immuno fluorescence studies indicate that overexpressed receptor is delivered to the vacuole. A mutant form of Vps10p, in which 157 residues of the 164-residue cytoplasmic tail domain have been deleted, missorts CPY a nd is degraded rapidly. Additional mutations in the carboxy-terminus o f Vps10p, including a deletion of a putative retention/recycling signa l (FYVF), also result in CPY missorting and PEP4-dependent receptor in stability. Because the cytoplasmic tail domain may interact with other factors, possibly VPS gene products, Vps10p stability was examined in a number of vps mutants. As was observed with the late Golgi protein Kex2p, Vps10p is unstable in a vps1 mutant. However, instability of Vp s10p is even more severe in the class E vps mutants. Double mutant ana lyses demonstrate that this rapid degradation is dependent upon vacuol ar proteases and a functional vacuolar ATPase. Fractionation studies o f Vps10p in class E vps mutant strains indicate that the turnover of V ps10p occurs in a compartment other than the vacuole. These data are c onsistent with a model in which the cytoplasmic tail of Vps10p directs cycling of the receptor between a late Golgi sorting compartment and a prevacuolar endosome-like compartment, an exaggerated form of which is present in the vps class E mutants.