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 > putrescine ∼ 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 > putrescine ∼ spermine. Experiments whit methylgiyoxal 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.