The Saccharomyces cerevisiae VPS23 (STP22) gene is implicated in the control of vesicle movement and quality of plasma membrane proteins. VPS23 mutants have defects either in removing defective membrane proteins such as alpha-mating factor receptor and arginine permease. The human ortholog TSG101 and its variants, isolated from tumor cells, do not substitute VPS23 in its ability to rescue the phenotype of defective plasma membrane proteins.