title: RecG Directs DNA Synthesis during Double-Strand Break Repair.
abstract: Homologous recombination provides a mechanism of DNA double-strand break repair (DSBR) that requires an intact, homologous template for DNA synthesis. When DNA synthesis associated with DSBR is convergent, the broken DNA strands are replaced and repair is accurate. However, if divergent DNA synthesis is established, over-replication of flanking DNA may occur with deleterious consequences. The RecG protein of Escherichia coli is a helicase and translocase that can re-model 3-way and 4-way DNA structures such as replication forks and Holliday junctions. However, the primary role of RecG in live cells has remained elusive. Here we show that, in the absence of RecG, attempted DSBR is accompanied by divergent DNA replication at the site of an induced chromosomal DNA double-strand break. Furthermore, DNA double-stand ends are generated in a recG mutant at sites known to block replication forks. These double-strand ends, also trigger DSBR and the divergent DNA replication characteristic of this mutant, which can explain over-replication of the terminus region of the chromosome. The loss of DNA associated with unwinding joint molecules previously observed in the absence of RuvAB and RecG, is suppressed by a helicase deficient PriA mutation (priA300), arguing that the action of RecG ensures that PriA is bound correctly on D-loops to direct DNA replication rather than to unwind joint molecules. This has led us to put forward a revised model of homologous recombination in which the re-modelling of branched intermediates by RecG plays a fundamental role in directing DNA synthesis and thus maintaining genomic stability.
authors.affiliation: Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Benura
authors.initials: B
authors.lastname: Azeroglu
authors.affiliation: Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Julia S P
authors.initials: JS
authors.lastname: Mawer
authors.affiliation: Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Charlotte A
authors.initials: CA
authors.lastname: Cockram
authors.affiliation: Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Martin A
authors.initials: MA
authors.lastname: White
authors.affiliation: Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: A M Mahedi
authors.initials: AM
authors.lastname: Hasan
authors.affiliation: Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Milana
authors.initials: M
authors.lastname: Filatenkova
authors.affiliation: Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: David R F
authors.initials: DR
authors.lastname: Leach
mesh_terms: D047369:Chromatin Immunoprecipitation; D002876:Chromosomes, Bacterial / Q000378:metabolism; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D004261:DNA Replication; D004269:DNA, Bacterial / Q000096:biosynthesis*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D011995:Recombination, Genetic
chemical_list: D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C071446:RecG protein, E coli