The binding of two dimers of IciA protein to the dnaA promoter 1P element enhances the binding of RNA polymerase to the dnaA promoter 1P.

Transcription of the dnaA gene from the promoter 1P has been shown to be activated in vitro and in vivo by the binding of IciA protein to two sites on the dnaA promoter region [Lee, Y. S., Kim, H., and Hwang, D. S. (1996) Mol. Microbiol . 19, 389-396; Lee, Y. S., and Hwang, D. S. (1997) J. Biol. Chem. 272, 83-88]. In vitro transcription assays using DNA fragments carrying variable combinations of two IciA binding sites revealed that IciA binding site I (IciA I site), which is located upstream of the promoter 1P, is responsible for the transcriptional activation. Binding of one dimeric IciA protein to the IciA I site is followed by binding of the second dimer. Two dimers of IciA protein, rather than one dimer, on the IciA I site appeared to enhance the binding of RNA polymerase to the promoter 1P, resulting in the activation of transcription from the promoter 1P.