Autoregulation of the dnaA gene of Escherichia coli K12.

Regulation of the dnaA gene, which codes for an essential factor for the initiation of replication from the chromosomal origin, was studied in vivo using transcriptional and translational gene fusions. We found that the dnaA gene was autoregulated over a 30-fold range by the activity of dnaA protein. Expression from the dnaA promoter region of a dnaA"lacZ fusion was inhibited up to sevenfold by surplus dnaA protein and was stimulated up to fivefold upon thermoinactivation of the mutant protein in five different dnaA(Ts) strains. The autoregulation was found to be exerted at transcription from the major dnaA promoter and was eliminated by deletion of sequences around position -65 of this promoter where a 9-bp sequence, which is also found four times in the chromosomal origin, is located.