A mutant plasma membrane ATPase, Pma1-10, is defective in stability at theyeast cell surface

Pma1 is a plasma membrane HT-ATPase whose activity at the cell surface is e ssential for cell viability. In this paper we describe a temperature-sensit ive pma1 allele, pma1-10 (with two point mutations in the first cytoplasmic loop of Pma1}, in which the newly synthesized mutant protein fails to rema in stable at the cell surface at 37 degreesC. Instead, Pma1-10 appears to u ndergo internalization for vacuolar degradation in a manner dependent on En d4, Vps27, Doa4, and Pep4. By contrast with wild-type Pma1, mutant Pma1-10 is hypophosphorylated and fails to associate with a Triton-insoluble fracti on at 37 degreesC, suggesting failure to enter lipid rafts. Kinetic analysi s reveals that, at the permissive temperature, newly synthesized Pma1-10 ac quires Triton-insolubility before becoming stabilized. We suggest that phos phorylation and lipid raft association may play important rotes in maintain ing protein stability at the plasma membrane.