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.
Rex
J H
JH
Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907.
Aronson
B D
BD
Somerville
R L
RL
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