Several routes of activation of the potassium uptake system of yeast.

K+ uptake in yeast is activated by glucose and other fermentable sugars, and by cytoplasmic acidification. In sugar kinase mutants, fermentable sugars and 2-deoxyglucose produced activation if the sugar could be phosphorylated, indicating that phosphorylation of the sugar is sufficient to trigger the activating pathway. Activation by cytoplasmic acidification was mimicked by neomycin, suggesting that a phosphatidylinositol-type pathway could be involved.