Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 78

Replication of a circular bacterial chromosome initiates at a unique origin of chromosomal replication, or oriC, and proceeds in both directions around the circle. On the E. coli chromosome, oriC is located at 84.3 min. As mentioned above, the place in DNA at which replication occurs is known as the replication fork. Two replication forks start at oriC and proceed around the circle until they meet and terminate chromosomal replication. The DNA polymerases responsible for replicating the leading and lagging strands associate as a single holoenzyme. However, there is no association between the DNA polymerases at the two DNA replication forks to help drive the separation of chromosomes, and therefore, other force-generating mechanisms must be at play. As discussed in “Termination of Chromosome Replication” below, some bacteria actively terminate replication at a unique site in the DNA; however, these systems are not widespread, and most bacteria terminate replication using an unknown mechanism or simply terminate DNA replication where the two replication forks meet. Each time the two replication forks proceed around the circle and meet, a round of replication has been completed, and two new DNAs, called the daughter DNAs, are generated.