title: Replication fork reversal after replication-transcription collision.
abstract: Replication fork arrest is a recognized source of genetic instability, and transcription is one of the most prominent causes of replication impediment. We analyze here the requirement for recombination proteins in Escherichia coli when replication-transcription head-on collisions are induced at a specific site by the inversion of a highly expressed ribosomal operon (rrn). RecBC is the only recombination protein required for cell viability under these conditions of increased replication-transcription collisions. In its absence, fork breakage occurs at the site of collision, and the resulting linear DNA is not repaired and is slowly degraded by the RecJ exonuclease. Lethal fork breakage is also observed in cells that lack RecA and RecD, i.e. when both homologous recombination and the potent exonuclease V activity of the RecBCD complex are inactivated, with a slow degradation of the resulting linear DNA by the combined action of the RecBC helicase and the RecJ exonuclease. The sizes of the major linear fragments indicate that DNA degradation is slowed down by the encounter with another rrn operon. The amount of linear DNA decreases nearly two-fold when the Holliday junction resolvase RuvABC is inactivated in recB, as well as in recA recD mutants, indicating that part of the linear DNA is formed by resolution of a Holliday junction. Our results suggest that replication fork reversal occurs after replication-transcription head-on collision, and we propose that it promotes the action of the accessory replicative helicases that dislodge the obstacle.
authors.affiliation: CNRS, Centre de Génétique Moléculaire, UPR3404, Gif-sur-Yvette, France.
authors.forename: Anne L
authors.initials: AL
authors.lastname: De Septenville
authors.forename: Stéphane
authors.initials: S
authors.lastname: Duigou
authors.forename: Hasna
authors.initials: H
authors.lastname: Boubakri
authors.forename: Bénédicte
authors.initials: B
authors.lastname: Michel
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D053938:DNA Fragmentation; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism; D004261:DNA Replication / Q000235:genetics*; D045566:DNA, Cruciform / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000235:genetics*; D043211:Exodeoxyribonuclease V / Q000235:genetics*; D005090:Exodeoxyribonucleases / Q000235:genetics; D045565:Holliday Junction Resolvases / Q000235:genetics; D059765:Homologous Recombination / Q000235:genetics; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D011938:Rec A Recombinases / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D045566:DNA, Cruciform; D029968:Escherichia coli Proteins; C075518:invA protein, Bacteria; D008780:Methyltransferases; C110074:23S rRNA m1G745 methyltransferase; D011938:Rec A Recombinases; D005090:Exodeoxyribonucleases; C489467:RecJ protein, E coli; D043211:Exodeoxyribonuclease V; C468322:exodeoxyribonuclease V, E coli; D045565:Holliday Junction Resolvases; D004265:DNA Helicases