Altered distribution of the yeast plasma membrane H+-ATPase as a feature of vacuolar H+-ATPase null mutants.

The effect of vacuolar H(+)-ATPase (V-ATPase) null mutations on the targeting of the plasma membrane H(+)-ATPase (Pma1p) through the secretory pathway was analyzed. Gas1p, which is another plasma membrane component, was used as a control for the experiments with Pma1p. Contrary to Gas1p, which is not affected by the deletion of the V-ATPase complex in the V-ATPase null mutants, the amount of Pma1p in the plasma membrane is markedly reduced, and there is a large accumulation of the protein in the endoplasmic reticulum. Kex2p and Gef1p, which are considered to reside in the post-Golgi vesicles, were suggested as required for the V-ATPase function; hence, their null mutant phenotype should have been similar to the V-ATPase null mutants. We show that, in addition to the known differences between those yeast phenotypes, deletions of KEX2 or GEF1 in yeast do not affect the distribution of Pma1p as the V-ATPase null mutant does. The possible location of the vital site of acidification by V-ATPase along the secretory pathway is discussed.