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 Escheric hia coli cells and is important for the defence against hydrogen perox ide. We found that dps mRNA levels are controlled by rpoS-encoded sigm a(S), the transcriptional activator OxyR and the histonelike IHF prote in. In exponentially growing cells, dps is induced by treatment with h ydrogen peroxide in an OxyR-dependent manner. This OxyR-dependent indu ction occurs only during log phase, although the OxyR protein is prese nt in stationary phase. In the stationary phase cells, dps is expresse d in a sigma(S)- and IHF-dependent manner. The purified OxyR and IHF p roteins are also shown to bind upstream of the dos promoter. Our resul ts suggest that the dps promoter is recognized by both sigma(70)-holoe nzyme and os-holoenzyme, since OxyR acts through sigma(70) and the sta rts of the OxyR- and sigma S-dependent transcripts are identical.