The tdh and serA operons of Escherichia coli: mutational analysis of the regulatory elements of leucine-responsive genes.
The tdh promoter of Escherichia coli is induced seven- to eightfold when cells are grown in the presence of exogenous leucine. A scheme was devised to select mutants that exhibited high constitutive expression of the tdh promoter. The mutations in these strains were shown to lie within a previously identified gene (lrp) that encodes Lrp (leucine-responsive regulatory protein). By deletion analysis, the site of action of Lrp was localized to a 25-bp region between coordinates -69 and -44 of the tdh promoter. Disruption of a 12-bp presumptive target sequence found in this region of tdh resulted in constitutively derepressed expression from the tdh promoter. Similar DNA segments (consensus, TTTATTCtNaAT) were also identified in a number of other promoters, including each of the Lrp-regulated promoters whose nucleotide sequence is known. The sequence of the promoter region of serA, an Lrp-regulated gene, was determined. No Lrp consensus target sequence was present upstream of serA, suggesting that Lrp acts indirectly on the serA promoter. A previously described mutation in a leucine-responsive trans-acting factor, LivR (J. J. Anderson, S. C. Quay, and D. L. Oxender, J. Bacteriol. 126:80-90, 1976), resulted in constitutively repressed expression from the tdh promoter and constitutively induced expression from the serA promoter. The possibility that LivR and Lrp are allelic is discussed.
Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907.
J H
JH
Rex
B D
BD
Aronson
R L
RL
Somerville
D000429:Alcohol Oxidoreductases / Q000235:genetics*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics*; D004252:DNA Mutational Analysis; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D007930:Leucine / Q000235:genetics*; D008969:Molecular Sequence Data; D009875:Operator Regions, Genetic; D009876:Operon; D033902:Periplasmic Binding Proteins; D011401:Promoter Regions, Genetic; D012694:Serine / Q000235:genetics*; D015534:Trans-Activators / Q000235:genetics
D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; C024913:LivK protein, E coli; D033902:Periplasmic Binding Proteins; D015534:Trans-Activators; D012694:Serine; D000429:Alcohol Oxidoreductases; C023159:L-threonine 3-dehydrogenase; D007930:Leucine