title: Escherichia coli Lrp (leucine-responsive regulatory protein) does not directly regulate expression of the leu operon promoter.
abstract: Studies by R. Lin et al. (J. Bacteriol. 174:1948-1955, 1992) suggested that the Escherichia coli leu operon might be a member of the Lrp regulon. Their results were obtained with a leucine auxotroph; in leucine prototrophs grown in a medium lacking leucine, there was little difference in leu operon expression between lrp(+) and lrp strains. Furthermore, when leuP-lacZ transcriptional fusions that lacked the leu attenuator were used, expression from the leu promoter varied less than twofold between lrp(+) and lrp strains, irrespective of whether or not excess leucine was added to the medium. The simplest explanation of the observations of Lin et al. is that the known elevated leucine transport capacity of lrp strains (S. A. Haney et al., J. Bacteriol. 174:108-115, 1992) leads to very high intracellular levels of leucine for strains grown with leucine, resulting in the superattenuation of leu operon expression.
authors.affiliation: Section of Biochemistry, Cornell University, Ithaca, New York 14853, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Landgraf
authors.forename: J A
authors.initials: JA
authors.lastname: Boxer
authors.forename: J M
authors.initials: JM
authors.lastname: Calvo
mesh_terms: D050539:3-Isopropylmalate Dehydrogenase; D000429:Alcohol Oxidoreductases / Q000096:biosynthesis; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D007930:Leucine / Q000096:biosynthesis*; D051756:Leucine-Responsive Regulatory Protein; D009154:Mutation; D009876:Operon; D011401:Promoter Regions, Genetic; D014157:Transcription Factors
chemical_list: D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C497278:Lrp protein, E coli; D014157:Transcription Factors; D051756:Leucine-Responsive Regulatory Protein; D000429:Alcohol Oxidoreductases; D050539:3-Isopropylmalate Dehydrogenase; D007930:Leucine