Organization of the replication initiation and termination sites on the E. coli chromosome. The origin of bidirectional replication is labeled oriC, and the two replication forks are represented by the DnaB helicases. Termination sites are labeled TerA through TerF. The locations of the termination sites are not to scale: the sites are located between 23 and 29 min (TerA, TerD, and TerE), 33 and 36 min (TerB and TerC), and at 48 min (TerF); thus these sites are spread over a long distance (1 min is approximately equal to 50 kb). The T shape of the termination site denotes the polarity of the site; replication forks meeting the flat side (top of the T) are arrested (that is, the clockwise fork will pass through sites TerE, TerD, and TerA, but will stop at TerC, TerB, or TerF). A protein called Tus binds to the Ter sites, and this binding stops DnaB (helicase) action.