Sterol control of the phosphatidylethanolamine-phosphatidylcholine conversion in the yeast mutant GL7

The relatively slow growth rate of the yeast mutant GL7, a sterol auxotroph, on medium containing cholesterol is markedly accelerated by supplementation with small amounts of ergosterol. Under these conditions (sterol synergism) cellular phospholipid synthesis is enhanced. We now find that one of the ergosterol-stimulated processes is the methylation of phosphatidylethanolamine to phosphatidylcholine. This is shown by comparing methyltransferase activities of membrane preparations derived from cells grown on either ergosterol, cholesterol, or the synergistic sterol pair. Incorporation of 32P from [gamma-32P]ATP into the yeast membranes is rapid and greater when ergosterol-grown cells rather than cholesterol-grown cells are the source of membranes.