oriC is 245 bp long and contains several conserved sequences: four 9-bp repeats (blue) and three 13-bp repeats (red). The orientation, spacing, and sequences of the 9-bp repeats are critical for function of oriC. The AT-richness of the 13-bp repeats is also crucial for function of oriC. DNA replication is initiated when oriC DNA wraps around a complex of 10-20 DnaA proteins. The wrapping denatures the AT-rich repeats. The denatured region of DNA is held open by the binding of SSB (single strand binding protein). DnaB helicase is loaded onto each strand in an ATP-dependent step requiring DnaA and DnaC. When DnaB is finally loaded onto DNA, DnaC is no longer complexed with DnaB.