title: Nitrogen regulation of the codBA (cytosine deaminase) operon from Escherichia coli by the nitrogen assimilation control protein, NAC.
abstract: Transcription of the cytosine deaminase (codBA) operon of Escherichia coli is regulated by nitrogen, with about three times more codBA expression in cells grown in nitrogen-limiting medium than in nitrogen-excess medium. Beta-galactosidase expression from codBp-lacZ operon fusions showed that the nitrogen assimilation control protein NAC was necessary for this regulation. In vitro transcription from the codBA promoter with purified RNA polymerase was stimulated by the addition of purified NAC, confirming that no other factors are required. Gel mobility shifts and DNase I footprints showed that NAC binds to a site centered at position -59 relative to the start site of transcription and that mutants that cannot bind NAC there cannot activate transcription. When a longer promoter region (positions -120 to +67) was used, a double footprint was seen with a second 26-bp footprint separated from the first by a hypersensitive site. When a shorter fragment was used (positions -83 to +67), only the primary footprint was seen. Nevertheless, both the shorter and longer fragments showed NAC-mediated regulation in vivo. Cytosine deaminase expression in Klebsiella pneumoniae was also regulated by nitrogen in a NAC-dependent manner. K. pneumoniae differs from E. coli in having two cytosine deaminase genes, an intervening open reading frame between the codB and codA orthologs, and a different response to hypoxanthine which increased cod expression in K. pneumoniae but decreased it in E. coli.
authors.affiliation: Department of Molecular Cellular and Developmental Biology, The University of Michigan, Ann Arbor, Michigan 48109-1048, USA.
authors.forename: Wilson B
authors.initials: WB
authors.lastname: Muse
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Rosario
authors.forename: Robert A
authors.initials: RA
authors.lastname: Bender
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins; D001483:Base Sequence; D043525:Cytosine Deaminase; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000502:physiology*; D015964:Gene Expression Regulation, Bacterial; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000378:metabolism*; D009700:Nucleoside Deaminases / Q000235:genetics* / Q000378:metabolism; D009876:Operon; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; C072712:NAC protein, bacteria; C489526:Nac protein, E coli; D014157:Transcription Factors; C075818:codB protein, E coli; D009700:Nucleoside Deaminases; D043525:Cytosine Deaminase; C468827:codA protein, E coli; D009584:Nitrogen