DNAA PROTEIN STIMULATES POLA GENE-EXPRESSION IN ESCHERICHIA-COLI

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