Catabolite regulation of two Escherichia coli operons encoding nitrite reductases: role of the Cra protein.
The Escherichia coli nir and nrf operons, which encode alternative nitrite reductases expressed during anaerobic growth, are subject to catabolite regulation. Transcription from the nir promoter is maximal when bacteria are grown in rich media such as Lennox broth supplemented with glucose. Conversely, expression of the nrf operon is suppressed by rich media, but stimulated during growth in minimal medium with glycerol and fumarate. The role of the catabolite repressor-activator (Cra) protein in catabolite regulation of the nir and nrf promoters was investigated. Transcription from the nir promoter was repressed by Cra when cells were grown in minimal medium with glycerol and fumarate. Crude protein extracts from a strain overproducing Cra encoded on a multicopy plasmid retarded a nir promoter fragment in a mobility shift assay, confirming that the observed Cra-dependent repression was due to the direct interaction of Cra with the regulatory region of the nir operon. Furthermore, the inclusion of fructose 1-phosphate, an effector of Cra DNA-binding activity, in the assay decreased the ability of Cra to retard the nir promoter fragment. In contrast, transcription from the nrf promoter was not regulated by Cra under any of the growth conditions tested.
Tyson
K
K
School of Biochemistry, University of Birmingham, Birmingham B15 2TT, UK.
Busby
S
S
Cole
J
J
D001426:Bacterial Proteins / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D004794:Enzyme Repression; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D029968:Escherichia coli Proteins; D005636:Fructosephosphates / Q000494:pharmacology; D015964:Gene Expression Regulation, Bacterial; D050898:Nitrite Reductase (NAD(P)H); D009572:Nitrite Reductases / Q000096:biosynthesis / Q000235:genetics*; D009876:Operon; D011401:Promoter Regions, Genetic; D011485:Protein Binding / Q000187:drug effects; D012097:Repressor Proteins / Q000378:metabolism*; D014158:Transcription, Genetic; D056968:Lac Repressors
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D005636:Fructosephosphates; D050898:Nitrite Reductase (NAD(P)H); D009572:Nitrite Reductases; D012097:Repressor Proteins; C489416:FruR protein, E coli; C068837:FruR protein, Bacteria; D056968:Lac Repressors; C032284:fructose-1-phosphate