Dissection of promoter sequences involved in transcriptional activation of the Escherichia coli replication origin.

The replication frequency of oriC plasmids in vivo is positively affected by specific transcripts running into oriC. These transcripts that activate oriC are initiated at a promoter of a gene coding for a 16kD protein. Genetic evidence is presented for binding of the initiation factor dnaA to a specific sequence (dnaA box) upstream of this promoter. Binding of the dnaA protein to this dnaA box regulates transcription initiation negatively. It was also demonstrated that binding of dnaA protein to the 16kD promoter region is essential to accomplish the actual activation event within the origin. Replication and incompatibility experiments suggest that dnaA protein is present within the activating transcription complex. The function of dnaA in this replication control mechanism is discussed.