REGULATION AND PH-DEPENDENT EXPRESSION OF A BILATERALLY TRUNCATED YEAST PLASMA-MEMBRANE H-ATPASE()

Constitutive, chromosomal expression of yeast pma1 deletion alleles in Saccharomyces cerevisiae yielded functional, truncated forms of the p lasma membrane H+-ATPase which were independently capable of supportin g wild type yeast growth rates. Deletion of 27 amino-terminal residues affected neither the enzyme's activity nor its responsiveness to chan ges in glucose metabolism. By contrast, removal of 18 carboxy-terminal amino acids produced an enzyme with a V-max that was relatively insen sitive to glucose-dependent metabolic status and with a K-m that was s ignificantly lower than that of the wild type enzyme. These effects we re exaggerated when the amino- and carboxy-terminal deletions were com bined in a bilaterally truncated H+-ATPase, suggesting that the amino terminus may have a subtle role in modulating ATPase activity. In pma1 Delta Delta cells cultured at pH 6, plasma membrane H+-ATPase levels were much lower than those in cells expressing a wild type ATPase. Inc reased expression levels could be achieved by growing the pma1 Delta D elta mutant at pH 3, a result that was at least partially due to a sus tained, elevated transcription of pma1 Delta Delta mRNA. Our observati ons suggest that intracellular proton balance can be maintained by reg ulation of the activity and/or quantity of H+-ATPase in the plasma mem brane. (C) 1998 Elsevier Science B.V. All rights reserved.