Induction and Repression in the S -Adenosylmethionine and Methionine Biosynthetic Systems of Saccharomyces cerevisiae

Abstract

Two methionine biosynthetic enzymes and the methionine adenosyltransferase are repressed in Saccharomyces cerevisiae when grown under conditions where the intracellular levels of S -adenosylmethionine are high. The nature of the co-repressor molecule of this repression was investigated by following the intracellular levels of methionine, S -adenosylmethionine, and S -adenosylhomocysteine, as well as enzyme activities, after growth under various conditions. Under all of the conditions found to repress these enzymes, there is an accompanying induction of the S -adenosylmethionine-homocysteine methyltransferase which suggests that this enzyme may play a key role in the regulation of S -adenosylmethionine and methionine balance and synthesis. S -methylmethionine also induces the methyltransferase, but unlike S -adenosylmethionine, it does not repress the methionine adenosyltransferase or other methionine biosynthetic enzymes tested.