Tight control of the amount of yeast plasma membrane ATPase during changes in growth conditions and gene dosage.

The activity of the plasma membrane ATPase in growing yeast is increased by low pH and by glucose, conditions which result in a higher demand for proton pumping. The amount of enzyme is not significatively modified under these conditions. The amount of ATPase is only slightly increased by introducing extra copies of its gene in autonomous plasmids. In addition, the expression of the ATPase gene in a multi-copy plasmid causes a reduction of the copy number of the plasmid and slows growth. Therefore, overexpression of the ATPase is detrimental for the cell, justifying a regulatory mechanism based on increasing the catalytic activity and not the amount of enzyme.