The dps promoter is activated by OxyR during growth and by IHF and σs in stationary phase

Dps is a non-specific DNA-binding protein abundant in starved Escherichia coli cells and is important for the defence against hydrogen peroxide. We found that dps mRNA levels are controlled by rpoS-encoded sigma S, the transcriptional activator OxyR and the histone-like IHF protein. In exponentially growing cells, dps is induced by treatment with hydrogen peroxide in an OxyR-dependent manner. This OxyR-dependent induction occurs only during log phase, although the OxyR protein is present in stationary phase. In the stationary phase cells, dps is expressed in a sigma S- and IHF-dependent manner. The purified OxyR and IHF proteins are also shown to bind upstream of the dps promoter. Our results suggest that the dps promoter is recognized by both sigma 70-holoenzyme and sigma S-holoenzyme, since OxyR acts through sigma 70 and the starts of the OxyR- and sigma S-dependent transcripts are identical.