Titration of DnaA protein by oriC DnaA-boxes increases dnaA gene expression in Escherichia coli.

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Abstract
Binding of the DnaA protein to its binding sites, the DnaA‐boxes (TTATCCACA), was measured by a simple physiological approach. The presence of extra DnaA‐boxes in growing cells leads to a derepression of dnaA gene expression, measured as beta‐galactosidase activity of a dnaA‐lacZ fusion polypeptide. Different DnaA‐boxes caused different degrees of derepression indicating that the DnaA protein requires sequences in addition to the DnaA‐box for efficient binding. The DnaA‐boxes in oriC might act cooperatively in binding of the DnaA protein. The derepressed levels of DnaA protein obtained in a strain carrying an oriC+‐pBR322 chimera were very high and sufficient to activate oriC on the chimeric plasmid, which was maintained at a copy number more than three times that of pBR322.