Replisome architecture and dynamics in Escherichia coli.

The field of DNA replication was launched upon discovery of the first DNA polymerase by Kornberg and Lehman (1, 2). DNA polymerase I displayed the novel and highly exciting property of template-directed enzymatic action, and like a split personality, DNApolymerase I could also degradeDNA, from either direction. Escherichia coli is now known to contain five different DNA polymerases. The chromosomal replicase is DNA polymerase III, while the damage-inducible DNA polymerases II, IV, and V play roles in DNA repair. DNA polymerase I is involved in both replication and repair and remains the most advanced model for the structure and function of DNA polymerase action. DNA polymerase III (pol III)2 functions in the context of a multiprotein apparatus called DNA pol III holoenzyme (reviewed in (3–5)). pol III holoenzyme contains 10 different proteins, which assort into three major functional units: 1) pol III core, 2) the sliding clamp, and 3) the / complex clamp loader. The holoenzyme contains two copies of the pol III core, which are connected by the attachment to one clamp loader. The holoenzyme functions within the context of a dynamic replisome containing pol III holoenzyme, a hexameric DnaB helicase, DnaGprimase, and SSB. During replisome function, contacts between these proteins are in a constant state of change. This review briefly summarizes the architecture and dynamic behavior of the E. coli replisome.