Transcription of rpoH, encoding the Escherichia coli heat-shock regulator sigma32, is negatively controlled by the cAMP-CRP/CytR nucleoprotein complex.
In Escherichia coli, the rpoH gene encoding the essential heat-shock regulator sigma32, is expressed in a complex manner. Transcription occurs from four promoters (P1, P3, P4 and P5) and is modulated by several factors including (i) two sigma factors (sigma70 and sigmaE); (ii) the global regulator CRP; and (iii) the DnaA protein. Here, a further dissection of the rpoH regulatory region has revealed that an additional transcription control exists that appears to link rpoH expression to nucleoside metabolism. The cAMP-CRP complex and the CytR anti-activator bind co-operatively to the promoter region forming a repression complex that overlaps the sigmaE-dependent P3 promoter and the sigma70-dependent P4 and P5 promoters. During steady-state growth conditions with glycerol as the carbon and energy source, transcription from P3, P4 and P5 is reduced approximately threefold by CytR, whereas transcription from the upstream promoter, P1, appears to be unaffected. Furthermore, in strains that slightly overproduce CytR, transcription from P3, P4 and P5 is reduced even further (approximately 10-fold), and repression can be fully neutralized by the addition of the inducer cytidine to the growth medium. In the induced state, P4 is the strongest promoter and, together with P3 and P5, it is responsible for most rpoH transcription (65-70%). At present, CytR has been shown to 'fine tune' transcription of two genes (rpoH and ppiA) that are connected with protein-folding activities. These findings suggest that additional assistance in protein folding is required under conditions in which CytR is induced (i.e. in the presence of nucleosides).
Kallipolitis
B H
BH
Department of Molecular Biology, Odense University, Denmark.
Valentin-Hansen
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D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002352:Carrier Proteins; D002874:Chromosome Mapping; D002373:Cyclic AMP Receptor Protein / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D006360:Heat-Shock Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D009698:Nucleoproteins / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000378:metabolism; D012808:Sigma Factor / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D002352:Carrier Proteins; D002373:Cyclic AMP Receptor Protein; C048425:CytR protein, E coli; D017931:DNA Primers; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; D009698:Nucleoproteins; D012097:Repressor Proteins; D012808:Sigma Factor; D014157:Transcription Factors; C069774:heat-shock sigma factor 32