Regulation of expression of the dnaA gene in Escherichia coli: role of the two promoters and the DnaA box.

The dnaA gene of Escherichia coli specifies a product that is a key element in the initiation of DNA replication. Expression of dnaA occurs from two promoters, 1P and 2P, which flank a DnaA protein binding site (DnaA box). In this paper we describe the effects of DnaA box mutations on transcription from the two promoters, measured with the use of dnaA-galK gene fusions. All of the mutations examined led to a five-fold increase in expression from the upstream promoter, 1P, suggesting that expression from this promoter is negatively autoregulated by binding of DnaA protein to the box. The same mutations led to a decrease in expression from promoter 2P, suggesting that the DnaA box plays a role in activating promoter 2P under normal conditions. Overproduction of DnaA protein, above normal physiological levels, led to decreased transcription from both promoters. We present evidence from analysis of both dnaA mRNA and DnaA protein that promoter 2P is subject to growth rate-dependent control and that this promoter, but not promoter 1P, is completely shut off in the stationary phase of growth.