The NsrR regulon of Escherichia coli K-12 includes genes encoding the hybrid cluster protein and the periplasmic, respiratory nitrite reductase.
Successful pathogens must be able to protect themselves against reactive nitrogen species generated either as part of host defense mechanisms or as products of their own metabolism. The regulatory protein NsrR (a member of the Rrf2 family of transcription factors) plays key roles in this stress response. Microarray analysis revealed that NsrR represses nine operons encoding 20 genes in Escherichia coli MG1655, including the hmpA, ytfE, and ygbA genes that were previously shown to be regulated by NsrR. Novel NsrR targets revealed by this study include hcp-hcr (which were predicted in a recent bioinformatic study to be NsrR regulated) and the well-studied nrfA promoter that directs the expression of the periplasmic respiratory nitrite reductase. Conversely, transcription from the ydbC promoter is strongly activated by NsrR. Regulation of the nrf operon by NsrR is consistent with the ability of the periplasmic nitrite reductase to reduce nitric oxide and hence protect against reactive nitrogen species. Gel retardation assays were used to show that both FNR and NarL bind to the hcp promoter. The expression of hcp and the contiguous gene hcr is not induced by hydroxylamine. As hmpA and ytfE encode a nitric oxide reductase and a mechanism to repair iron-sulfur centers damaged by nitric oxide, the demonstration that hcp-hcr, hmpA, and ytfE are the three transcripts most tightly regulated by NsrR highlights the possibility that the hybrid cluster protein, HCP, might also be part of a defense mechanism against reactive nitrogen stress.
Filenko
Nina
N
School of Biosciences, University of Birmingham, Birmingham B15 2TT, United Kingdom.
Spiro
Stephen
S
Browning
Douglas F
DF
Squire
Derrick
D
Overton
Tim W
TW
Cole
Jeff
J
Constantinidou
Chrystala
C
D002678:Chimera; D003574:Cytochrome c Group / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D048168:Escherichia coli K12 / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D005809:Genes, Regulator; D007506:Iron-Sulfur Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D033903:Periplasmic Proteins / Q000235:genetics; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D026361:Reactive Nitrogen Species / Q000378:metabolism*; D018085:Regulon / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic
D003574:Cytochrome c Group; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C060704:FNR protein, E coli; D007506:Iron-Sulfur Proteins; D033903:Periplasmic Proteins; D026361:Reactive Nitrogen Species; D014157:Transcription Factors; C069780:NarL protein, E coli; C022302:cytochrome C-552