title: Tandem repeat recombination induced by replication fork defects in Escherichia coli requires a novel factor, RadC.
abstract: DnaB is the helicase associated with the DNA polymerase III replication fork in Escherichia coli. Previously we observed that the dnaB107(ts) mutation, at its permissive temperature, greatly stimulated deletion events at chromosomal tandem repeats. This stimulation required recA, which suggests a recombinational mechanism. In this article we examine the genetic dependence of recombination stimulated by the dnaB107 mutation. Gap repair genes recF, recO, and recR were not required. Mutations in recB, required for double-strand break repair, and in ruvC, the Holliday junction resolvase gene, were synthetically lethal with dnaB107, causing enhanced temperature sensitivity. The hyperdeletion phenotype of dnaB107 was semidominant, and in dnaB107/dnaB+ heterozygotes recB was partially required for enhanced deletion, whereas ruvC was not. We believe that dnaB107 causes the stalling of replication forks, which may become broken and require repair. Misalignment of repeated sequences during RecBCD-mediated repair may account for most, but not all, of deletion stimulated by dnaB107. To our surprise, the radC gene, like recA, was required for virtually all recombination stimulated by dnaB107. The biochemical function of RadC is unknown, but is reported to be required for growth-medium-dependent repair of DNA strand breaks. Our results suggest that RadC functions specifically in recombinational repair that is associated with the replication fork.
authors.affiliation: Department of Biology and Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02454-9110, USA.
authors.forename: C J
authors.initials: CJ
authors.lastname: Saveson
authors.forename: S T
authors.initials: ST
authors.lastname: Lovett
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D004265:DNA Helicases / Q000235:genetics; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000235:genetics; D053488:DnaB Helicases; D004706:Endodeoxyribonucleases / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D005799:Genes, Dominant; D008957:Models, Genetic; D016296:Mutagenesis; D010641:Phenotype; D011938:Rec A Recombinases / Q000235:genetics; D011995:Recombination, Genetic; D020080:Tandem Repeat Sequences
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C081006:RecO protein, E coli; C489318:RecR protein, E coli; C489340:recF protein, E coli; C069806:ruvC protein, E coli; C065831:RecR protein, Bacteria; C074495:yicR protein, E coli; C066218:recF protein, Bacteria; D011938:Rec A Recombinases; D004706:Endodeoxyribonucleases; D004265:DNA Helicases; D053488:DnaB Helicases