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Graphical abstract Highlights • Cryo-EM structures of Escherichia coli DNA polymerase III complexes. • Bacterial polymerases quickly exchange at replication forks. • Bacterial replisomes can work in a decoupled and uncoordinated manner. • Replisome speed determines fork arrest efficiency in replication termination. Bacterial replisomes are dynamic multiprotein DNA replication machines that are inherently difficult for structural studies. However, breakthroughs continue to come. The structures of Escherichia coli DNA polymerase III (core)–clamp–DNA subcomplexes solved by single-particle cryo-electron microscopy in both polymerization and proofreading modes and the discovery of the stochastic nature of the bacterial replisomes represent notable progress. The structures reveal an intricate interaction network in the polymerase–clamp subassembly, providing insights on how replisomes may work. Meantime, ensemble and single-molecule functional assays and fluorescence microscopy show that the bacterial replisomes can work in a decoupled and uncoordinated way, with polymerases quickly exchanging and both leading-strand and lagging-strand polymerases and the helicase working independently, contradictory to the elegant textbook view of a highly coordinated machine. [ABSTRACT FROM AUTHOR]

Rolling-circle DNA amplification is a powerful tool employed in biotechnology to produce large from small amounts of DNA. This mode of DNA replication proceeds via a DNA topology that resembles a replication fork, thus also providing experimental access to the molecular mechanisms of DNA replication. However, conventional templates do not allow controlled access to multiple fork topologies, which is an important factor in mechanistic studies. Here we present the design and production of a rolling-circle substrate with a tunable length of both the gap and the overhang, and we show its application to the bacterial DNA-replication reaction. [ABSTRACT FROM AUTHOR]

Recent studies of bacterial DNA replication have led to a picture of the replisome as an entity that freely exchanges DNA polymerases and displays intermittent coupling between the helicase and polymerase(s). Challenging the textbook model of the polymerase holoenzyme acting as a stable complex coordinating the replisome, these observations suggest a role of the helicase as the central organizing hub. We show here that the molecular origin of this newly found plasticity lies in the 500-fold increase in strength of the interaction between the polymerase holoenzyme and the replicative helicase upon association of the primase with the replisome. By combining in vitro ensemble-averaged and single-molecule assays, we demonstrate that this conformational switch operates during replication and promotes recruitment of multiple holoenzymes at the fork. Our observations provide a molecular mechanism for polymerase exchange and offer a revised model for the replication reaction that emphasizes its stochasticity. There are at least two functional modes of interaction of Pol III and DnaB on DNA The interaction between the CLC and DnaB strengthens ∼500-fold upon DnaG binding A single copy of the τ subunit in the CLC is responsible for binding DnaB Multiple Pol IIIs can be at the fork, subject to the status of DnaB-DnaG interaction Monachino et al. show that dynamic interaction of the Escherichia coli DnaG primase and DnaB helicase affects the stability of the replisome and the cycling of DNA polymerase III complexes at the replication fork through a conformational switch in DnaB that toggles its affinity for the polymerase. [ABSTRACT FROM AUTHOR]