title: A new methionine locus, metR, that encodes a trans-acting protein required for activation of metE and metH in Escherichia coli and Salmonella typhimurium.
abstract: We isolated an Escherichia coli methionine auxotroph that displays a growth phenotype similar to that of known metF mutants but has elevated levels of 5,10-methylenetetrahydrofolate reductase, the metF gene product. Transduction analysis indicates that the mutant carries normal metE, metH, and metF genes; the phenotype is due to a single mutation, eliminating the possibility that the strain is a metE metH double mutant; and the new mutation is linked to the metE gene by P1 transduction. Plasmids carrying the Salmonella typhimurium metE gene and flanking regions complement the mutation, even when the plasmid-borne metE gene is inactivated. Enzyme assays show that the mutation results in a dramatic decrease in metE gene expression, a moderate decrease in metH gene expression, and a disruption of the metH-mediated vitamin B12 repression of the metE and metF genes. Our evidence suggests that the methionine auxotrophy caused by the new mutation is a result of insufficient production of both the vitamin B12-independent (metE) and vitamin B12-dependent (metH) transmethylase enzymes that are necessary for the synthesis of methionine from homocysteine. We propose that this mutation defines a positive regulatory gene, designated metR, whose product acts in trans to activate the metE and metH genes.
mesh_terms: D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase / Q000235:genetics*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D005798:Genes, Bacterial; D005809:Genes, Regulator; D005816:Genetic Complementation Test; D008715:Methionine / Q000096:biosynthesis*; D008780:Methyltransferases / Q000235:genetics*; D009154:Mutation; D012486:Salmonella typhimurium / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D014161:Transduction, Genetic
chemical_list: D008715:Methionine; D008780:Methyltransferases; D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; C022725:5-methyltetrahydropteroyltriglutamate-homocysteine S-methyltransferase