Figure 2. Organization of the Caulobacter chromosomal origin of replication (Cori).

The Cori carries two classes of DnaA binding sites: G-boxes (G1 and G2; orange arrows) of moderate affinity and W-boxes (W1–W5; green arrows) of low affinity. Note that the G2 box overlaps one of the CtrA binding sites (red squares), suggesting that DnaA-ATP may compete with CtrA when binding to the Cori. The Cori also carries an IHF binding site (blue square) and five GANTC sites (fuchsia color; –CH₃) that are methylated by the CcrM DNA methyltransferase. IHF may promote the opening of the DNA double helix at the AT-rich region (purple box) when DnaA-ATP is bound to the Cori. In addition, the transcriptional start sites (TSS; represented by a thin black arrow) for three RNAs are located in the Cori: the duf299 (CCNA_00001) and hemE mRNAs and the CCNA_R0094 small non-coding RNA. Transcription starting at these TSS might influence initiation.