DnaA protein stimulates polA gene expression in Escherichia coli

The polA gene of Escherichia coli encodes DNA polymerase I that is involved in DNA replication and repair. Despite the wide knowledge about structure and function of DNA polymerase I, there is little insight into the regulatory mechanisms involved in polA expression. DnaA is the initiator protein for DNA replication in E. coli. There are two putative DnaA-binding sites within the extended promoter region of polA. In this work we studied the influence of altered levels of DnaA protein on polA expression. We found that DnaA overproduction increases polA expression in stationary-phase cultures. The stimulation effect was independent of rpoS, which encodes the sigma factor for stationary-phase-inducible genes. However, it was modulated by ppGpp. Comparative S1 analyses revealed that the induction was based on transcriptional stimulation. Footprinting experiments demonstrated that DnaA binds only to the proximal DnaA box near the polA promoter. These results suggest an additional role for DnaA as transcriptional activator of polA at least under certain physiological conditions.