Competition between NarL-dependent activation and Fis-dependent repression controls expression from the Escherichia coli yeaR and ogt promoters

Derrick J P Squire , Meng Xu , Jeffrey A Cole , Stephen J W Busby (1) , Douglas F Browning

1 School of Biosciences

The Escherichia coli NarL protein is a global gene regulatory factor that activates transcription at many target promoters in response to nitrate and nitrite ions. Although most NarL-dependent promoters are also co-dependent on a second transcription factor, FNR, two targets, the yeaR and ogt promoters are activated by NarL alone with no involvement of FNR. Biochemical and genetic studies presented here show that activation of the yeaR promoter is dependent on the binding of NarL to a single target centred at position 43.5, whilst activation at the ogt promoter requires NarL binding to tandem DNA targets centred at position -45.5 and -78.5. NarL dependent activation at both the yeaR and ogt promoters is decreased in rich medium and this depends on Fis, a nucleoid-associated protein. DNAse I footprinting studies identified Fis binding sites that overlap the yeaR promoter NarL site at position -43.5, and the ogt promoter NarL site at position -78.5, and suggest that Fis represses both promoters by displacing NarL. The ogt gene encodes an O6-alkylguanine DNA alkyltransferase and, hence, this is the first report of expression of a DNA repair function being controlled by nitrate ions.

Mots clés: Life Sciences

Derrick J P Squire, Meng Xu, Jeffrey A Cole, Stephen J W Busby, Douglas F Browning. Competition between NarL-dependent activation and Fis-dependent repression controls expression from the Escherichia coli yeaR and ogt promoters. Biochemical Journal, 2009, 420 (2), pp.249-257. ⟨10.1042/BJ20090183⟩. ⟨hal-00479159⟩