Proliferation of intracellular structures upon overexpression of the PMA2 ATPase in Saccharomyces cerevisiae.

The PMA2 gene is a presumed isogene of the PMA1 gene, encoding the major yeast plasma membrane H(+)-ATPase. When controlled by its own promoter, PMA2 in multiple copies does not complement a deficient PMA1 gene. Under the control of the PMA1 promoter, however, and expressed on a centromeric plasmid in yeast strains specially designed for stable expression, the PMA2 gene replaces the PMA1 gene to some extent, allowing growth on standard medium but not on acidic media. Plasma membranes of cells expressing only the PMA2 enzyme display low ATPase activity correlating with low amounts of PMA2 protein. This low activity is maintained throughout growth and does not increase when overexpression is favored by increased gene dosage. Immunoelectron microscopy reveals a dramatic proliferation of intracellular structures (probably endoplasmic reticulum) in which overexpressed PMA2 protein accumulates. Overexpression of PMA1 ATPase causes a similar phenomenon, but quantitative effects are lower compared to PMA2. These results indicate that the PMA2 gene encodes a functional plasma membrane H(+)-ATPase and suggest a specific control of the intracellular traffic of plasma membrane ATPase.