The replication origin in the bacterium Escherichia coli is called oriC. The name combines “origin” with the letter C, distinguishing the chromosomal origin from replication origins found on plasmids and other DNA molecules.
E. coli has a single circular chromosome, and replication begins at oriC before proceeding bidirectionally. The region contains multiple binding sites for the initiator protein DnaA. When active DnaA accumulates, it binds these sites, bends and organizes the DNA, and promotes local strand separation in an adjacent AT-rich region.
After the origin opens, helicase-loading proteins recruit the DnaB helicase, while primase and DNA polymerase III establish the replication forks. A common mix-up is oriT, which is the transfer origin used during bacterial conjugation, and oriV, a term used for plasmid vegetative replication origins. oriS is associated with certain viral systems, not the standard E. coli chromosomal origin.