Activation of the Escherichia coli nitrate reductase (narGHJI) operon by NarL and Fnr requires integration host factor.
Integration host factor protein (IHF) was shown to be required for Fnr- and NarL-dependent activation of the nitrate reductase (narGHJI) operon of Escherichia coli in response to nitrate availability and anaerobiosis. Using a narG-lacZ reporter fusion to evaluate narGHJI expression in vivo both the nitrate and anaerobic dependent controls were severely impaired in a himA mutant compared with the wild type strain. IHF was also required for Fnr-independent anaerobic control of narGHJI expression. In vitro, purified IHF protein was shown to bind to a narG promoter fragment with an apparent dissociation value of 5 nM by use of a gel shift assay. DNase I footprinting studies revealed that IHF protects a 37-base pair region centered 125 base pairs 5' of the narG transcription site. These studies suggest that the IHF protein performs a DNA bending function at the narG promoter to allow nitrate-dependent activation by the NarL regulatory protein, and second, it enhances the Fnr-dependent expression from the narG promoter under anaerobic cell growth conditions. A model whereby three transcriptional activators, NarL, IHF, and Fnr, induce expression of a sigma 70-dependent promoter for the narGHJI operon is discussed.
Schröder
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Department of Microbiology and Molecular Genetics, University of California, Los Angeles 90024.
Darie
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Gunsalus
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D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D034982:Integration Host Factors; D007506:Iron-Sulfur Proteins; D007700:Kinetics; D008969:Molecular Sequence Data; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000235:genetics* / Q000378:metabolism; D009876:Operon; D010957:Plasmids; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014161:Transduction, Genetic; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C060704:FNR protein, E coli; D034982:Integration Host Factors; D007506:Iron-Sulfur Proteins; D011993:Recombinant Fusion Proteins; C069780:NarL protein, E coli; D009565:Nitrate Reductases; D050901:Nitrate Reductase; D001616:beta-Galactosidase