Article

The Disposition of Nascent Strands at Stalled Replication Forks Dictates the Pathway of Replisome Loading during Restart

Program in Molecular Biology, Weill Graduate School of Medical Sciences, Cornell University, New York, New York 10021, USA.
Molecular Cell (Impact Factor: 14.46). 04/2005; 17(5):733-43. DOI: 10.1016/j.molcel.2005.01.019
Source: PubMed

ABSTRACT Rescue of arrested and collapsed replication forks is essential for maintenance of genomic integrity. One system for origin of replication-independent loading of the DnaB replicative helicase and subsequent replisome reassembly requires the structure-specific recognition factor PriA and the assembly factors PriB and DnaT. Here, we provide biochemical evidence for an alternate system for DnaB loading that requires only PriC. Furthermore, the choice of which system is utilized during restart is dictated by the nature of the structure of the stalled replication fork. PriA-dependent reactions are most robust on fork structures with no gaps in the leading strand, such as is found at the junction of a D loop, while the PriC-dependent system preferentially utilizes fork structures with large gaps in the leading strand. These observations suggest that the type of initial damage on the DNA template and how the inactivated fork is processed ultimately influence the choice of enzymatic restart pathway.

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    • "The importance of this replisome reassembly is underlined by the inviability of cells lacking PriA and a second structure-specific initiator PriC (Sandler 2000). PriA and PriC have complementary DNA substrate specificities, binding preferentially to forked DNA with and without a leading strand present at the branch point, respectively (Heller and Marians 2005b). The inviability of cells lacking both enzymes provides direct evidence for the low probability of replisomes assembled at oriC being able to complete chromosome duplication. "
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    • "Standard pathways for homologous recombination (RecBC and RecFOR) involve early events that process breaks and gaps leading to RecA-catalyzed strand invasion. This produces Holliday junctions that are moved on recombining duplexes by RuvAB (Heller and Marians 2005; reviewed by West 2003). The later events that stabilize and ultimately resolve these Holliday structures are achieved by two alternative enzymes: (1) the RuvABC resolvasome and (2) the RecG branch-migration enzyme (Benson et al. 1991; Wardrope and Leach 2009). "
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    • "Once DnaB has been loaded, the DNA polymerase III replisome and DNA primase are believed to reassemble automatically, via interactions with DnaB. E. coli uses two systems for replication restart, which depend on the nature of the substrates presented (Heller and Marians, 2005). For structures in which a 3 end, equivalent to the newly synthesized leading strand, abuts the fork, a PriA system is used to recruit DnaB and its escort proteins DnaC and DnaT. "
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