DNA loop formation between Nag repressor molecules bound to its two operator sites is necessary for repression of the nag regulon of Escherichia coli in vivo.
Binding sites for the Nag repressor overlap the transcription start sites of the divergent nagE and nagB genes, such that the centres of the sites are separated by nine turns of the B-DNA helix. Mutations which prevent repressor binding to either site or alter the phasing of the binding sites result in simultaneous derepression of both genes. An additional mutation which restores the phasing of the two sites permits repression. These observations show that repression is the result of co-operative binding of the repressor to its two sites, resulting in the formation of a loop of DNA.
Plumbridge
J
J
Institut de Biologie Physico-chimique (URA1139), Paris, France.
Kolb
A
A
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002352:Carrier Proteins; D000242:Cyclic AMP / Q000378:metabolism; D002373:Cyclic AMP Receptor Protein / Q000378:metabolism; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D009875:Operator Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D018085:Regulon; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors
D001426:Bacterial Proteins; D002352:Carrier Proteins; D002373:Cyclic AMP Receptor Protein; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C067862:nagC protein, E coli; D000242:Cyclic AMP