CATABOLITE INACTIVATION OF THE YEAST MALTOSE TRANSPORTER OCCURS IN THE VACUOLE AFTER INTERNALIZATION BY ENDOCYTOSIS

The maltose transporter of Saccharomyces cerevisiae is rapidly degrade d during fermentation in the absence of a nitrogen source. The locatio n and mechanism of degradation of the transporter have been investigat ed. Using mutants defective in endocytosis, we have shown that degrada tion of this transporter requires internalization by endocytosis. In a ddition, studies of mutants defective in proteasome or vacuolar proteo lysis revealed that degradation occurs iii the vacuole and is independ ent of proteasome function. The results also revealed that degradation of the maltose transporter requires Sec18p and raised the question of whether in the absence of Sec18p activity the internalized maltose tr ansporter is recycled back to the plasma membrane.