Regulation of Methionine Synthesis in Escherichia coli: Effect of metJ Gene Product and S−adenosylmethionine on the Expression of the metF Gene

The regulation of the expression of the Escherichia coli metF gene, which codes for 5,10−methylenetetrahydrofolate reductase (EC 1.1.99.15), has been investigated by using a simplified DNA−directed in vitro system that measures the formation of the first dipeptide (fMet−Ser) of the gene product. The synthesis of fMet−Ser directed by a plasmid containing the metF gene is specifically inhibited by metJ protein (repressor protein). S−Adenosylmethionine enhances the inhibition by the metJ protein of metF gene expression. The inhibition by the metJ protein is at the level of transcription and the results suggest that S−adenosylmethionine is functioning as an allosteric effecto