Regulation of transcription of the chromosomaldnaA gene ofEscherichia coli

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Abstract
By comparative S1 analysis we investigated the in vivo regulation of transcription of the chromosomaldnaA gene coding for a protein essential for the initiation of replication at the chromosomal origin. Inactivation of the protein indnaA mutants results in derepression, whereas excess DnaA protein (presence of a DnaA overproducing plasmid) leads to repression ofdnaA transcription. BothdnaA promoters are subject to autoregulation allowing modulation of transcriptional efficiency by at least 20-fold. Increasing the number oforiC sequences (number of DnaA binding sites) in the cell by introducingoriC plasmids leads to a derepression of transcription. Autoregulation and binding tooriC suggest that the DnaA protein exerts a major role in the regulation of the frequency of initiation atoriC. The efficiency of transcription of thednaA2 promoter is reduced in the absence ofdam methylation, which is involved in the regulation oforiC replication.