THE DPS PROMOTER IS ACTIVATED BY OXYR DURING GROWTH AND BY IHF AND A SIGMA(S) 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 histonelike 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 dos promoter. Our results suggest that the dps promoter is recognized by both sigma(70)-holoenzyme and os-holoenzyme, since OxyR acts through sigma(70) and the starts of the OxyR- and sigma S-dependent transcripts are identical.