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 maj or yeast plasma membrane H+-ATPase. When controlled by its own promote r, PMA2 in multiple copies does not complement a deficient PMA1 gene. Under the control of the PMA1 promoter, however, and expressed on a ce ntromeric plasmid in yeast strains specially designed for stable expre ssion, the PMA2 gene replaces the PMA1 gene to some extent, allowing g rowth on standard medium but not on acidic media. Plasma membranes of cells expressing only the PMA2 enzyme display low ATPase activity corr elating with low amounts of PMA2 protein. This low activity is maintai ned throughout growth and does not increase when overexpression is fav ored by increased gene dosage. Immunoelectron microscopy reveals a dra matic proliferation of intracellular structures (probably endoplasmic reticulum) in which overexpressed PMA2 protein accumulates. Overexpres sion of PMA1 ATPase causes a similar phenomenon, but quantitative effe cts are lower compared to PMA2. These results indicate that the PMA2 g ene encodes a functional plasma membrane H+-ATPase and suggest a speci fic control of the intracellular traffic of plasma membrane ATPase.