DNA Replication

DNA replication in Escherichia coli is a tightly regulated, multienzyme process that ensures that as cells divide, each new cell receives an exact copy of the genetic blueprint. There are regulatory mechanisms that prevent premature rounds of DNA synthesis before the entire chromosome has been replicated. The E. coli chromosome is circular, and replication is bidirectional, meaning two replication forks start at a defined location, oriC, proceed around the chromosome in opposite directions, and meet at a specific region called the terminus. The primary replicative polymerase is Pol III, an asymmetric complex that synthesizes DNA in the 5'-3' direction, and requires a primer, which is synthesized by primase. Pol III synthesizes continuously on the leading strand template and discontinuously on the lagging strand template. The nascent, lagging strand fragments are joined together by Pol I and DNA ligase. Finally, a regulatory mechanism is in place to terminate replication as the two replication forks meet, roughly half way around the chromosome, and to do so without skipping or duplicating any genetic information. Structural analysis of the many proteins involved in DNA replication has provided many details of how this complicated process occurs.