title: The leucine regulon of Escherichia coli K-12: a mutation in rblA alters expression of L-leucine-dependent metabolic operons.
abstract: We have isolated and characterized a highly pleiotropic Escherichia coli mutant affected in the activity of a number of enzymes involved in different metabolic pathways, all of which are regulated by leucine. Selected for its ability to grow with L-serine as sole carbon source, the rbl-1::Tn10 mutant had high levels of L-serine deaminase activity (due to increased transcription of the structural gene) and of another amino acid-degrading enzyme, L-threonine dehydrogenase, and decreased transcription of the operons serA and ilvIH, coding for biosynthetic enzymes. The rbl mutation suppressed the slow growth of a metK mutant, deficient in S-adenosylmethionine synthetase. Furthermore, metK mutants spontaneously accumulated faster-growing rbl-like derivatives, and a commonly used metK strain, RG62, carries such a mutation. The rbl gene is located near 20 min on the E. coli genetic map. All phenotypes of the rbl mutant could be observed in rbl+ strains cultivated in the presence of L-leucine, and exogenous L-leucine had little further effect on the rbl strains. We propose that the rbl gene product is the regulator of a global response to leucine.
authors.affiliation: Department of Biological Sciences, Concordia University, Montreal, Quebec, Canada.
authors.forename: L R
authors.initials: LR
authors.lastname: Tuan
authors.forename: R
authors.initials: R
authors.lastname: D'Ari
authors.forename: E B
authors.initials: EB
authors.lastname: Newman
mesh_terms: D000429:Alcohol Oxidoreductases / Q000235:genetics / Q000378:metabolism; D004251:DNA Transposable Elements; D004926:Escherichia coli / Q000235:genetics*; D005809:Genes, Regulator; D005838:Genotype; D012695:L-Serine Dehydratase / Q000235:genetics / Q000378:metabolism; D007930:Leucine / Q000378:metabolism*; D008716:Methionine Adenosyltransferase / Q000235:genetics; D009154:Mutation; D009876:Operon; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D004251:DNA Transposable Elements; D000429:Alcohol Oxidoreductases; C023159:L-threonine 3-dehydrogenase; D008716:Methionine Adenosyltransferase; D001616:beta-Galactosidase; D012695:L-Serine Dehydratase; D007930:Leucine