Induction of Choline Transport and Its Role in the Stimulation of the Incorporation of Choline into Phosphatidylcholine by Polyamines in a Polyamine Auxotroph of Saccharomyces cerevisiae

Abstract

1. A mutant of Saccharomyces cerevisiae, defective in ornithine decarboxylase, was isolated. A prolonged culture of the mutant in a polyamine-free medium resulted in a great decrease in the polyamine content and in cessation of growth. The addition of polyamines to the culture induced the growth after a lag period of 5--6.5 h. The growth rate in the presence of polyamine was comparable to that of the wild-type strain. The effectiveness of polyamines was as follows: spermidine greater than putrescine approximately equal to spermine. 2. Phosphatidylcholine-synthesizing activity during the lag phase of growth was determined by measuring the rate of incorporation of [14C]choline into phosphatidylcholine. The incorporation rate was markedly increased with time by polyamine prior to the initiation of cell division. Polyamines were effective in the following order: spermidine greater than putrescine approximately equal to spermine. Experiments with methylglyoxal bis(guanylhydrazone), an inhibitor of S-adenosylmethionine decarboxylase, showed that putrescine stimulates cell growth and choline incorporation into phosphatidylcholine after it has been converted into spermidine in the cell. 3. The induction of the choline transport system was shown to be responsible for the increase in the rate of incorporation of [14C]choline into phosphatidylcholine effected by polyamines. A low concentration of cycloheximide completely prevented the induction of choline transport by polyamines. The levels of the CDP-choline pathway enzymes such as choline kinase, cholinephosphate cytidyltransferase and cholinephosphotransferase were not significantly changed.