Replication Origin of E. coli and the Mechanism of Initiation

Abstract

Synopsis The process of DNA replication can be formally divided into the stages of initiation, the elongation of nascent DNA, and termination. In E. coli, DNA replication initiates at a specific location (oriC) on the circular duplex chromosome. This site is where the replication fork machinery is assembled, leading to duplication of the E. coli chromosome. At oriC, specific biochemical events must take place in a step-wise manner in order to establish the enzymatic machinery that will operate at a replication fork. The first step involves the recognition of DNA sequence elements in oriC by the replication initiator (DnaA). Its interaction with these DNA sequences leads to the assembly of a DnaA oligomer that unwinds a region within oriC. DnaA then interacts with DnaB in a complex with DnaC to load the replicative DNA helicase (DnaB) onto the single-stranded DNA in the unwound region (see " ▶ Elongation: Primases and Helicases " by Soultanas and Bolt in this volume). After helicase loading and its activation, involving the binding of primase (DnaG) to DnaB and primer formation, the primers are utilized by DNA polymerase III holoenzyme for DNA synthesis and duplication of the E. coli chromosome.