Compensatory Internalization of Pma1 in V-ATPase Mutants in Requires Calcium- and Glucose-Sensitive Phosphatases.

Loss of V-ATPase activity in organelles, whether through V-ATPase inhibition or V-ATPase () mutations, triggers a compensatory downregulation of the essential plasma membrane proton pump Pma1 in We have previously determined that the α-arrestin Rim8 and ubiquitin ligase Rsp5 are essential for Pma1 ubiquination and endocytosis in response to loss of V-ATPase activity. Here, we show that Pma1 endocytosis in V-ATPase mutants does not require Rim101 pathway components upstream and downstream of Rim8, indicating that Rim8 is acting independently in Pma1 internalization. We find that two phosphatases, the calcium-responsive phosphatase calcineurin and the glucose-sensitive phosphatase Glc7 (PP1), and one of the Glc7 regulatory subunits Reg1, exhibit negative synthetic genetic interactions with mutants, and demonstrate that both phosphatases are essential for ubiquitination and endocytic downregulation of Pma1 in these mutants.