title: In vivo evidence for a recA-independent recombination process in Escherichia coli that permits completion of replication of DNA containing UV damage in both strands.
abstract: We have investigated recombination mechanisms promoting the completion of replication in the face of unrepaired DNA damage by transforming an isogenic set of uvrA6 excision-defective Escherichia coli strains with pUC-based plasmids in which each strand carried, at staggered positions, a single thymine-thymine pyrimidine (6-4) pyrimidinone lesion. The distance between the lesions was 28 or 8 bp in one orientation relative to the unidirectional ColE1 origin of replication or, in the other orientation, 30 or 10 bp. C-C mismatches placed opposite each of the T-T photoproducts permit unambiguous detection of the three events that can lead to the completion of replication: sister-strand recombination, translesion replication (TR) on the leading strand, and TR on the lagging strand. We find that E. coli possesses a largely constitutive, recA-independent sister-strand recombination mechanism that allows 9% or more of these severely compromised plasmids to be fully replicated. In one orientation, such recombination depends partly on recG and priA but not on ruvA, ruvB, ruvC, or mutS and is largely independent of recF. In the other orientation, recombination is dependent on none of the genes. The strains used did not contain the cryptic phage encoding recET, which encodes enzymes that promote interplasmid recombination. The nature of the recA-independent recombination mechanism is not known but could perhaps result from a template-strand-switching, or copy choice, process.
authors.affiliation: Department of Biochemistry and Biophysics, University of Rochester School of Medicine & Dentistry, Rochester, NY 14642, USA.
authors.forename: Ali I
authors.initials: AI
authors.lastname: Ozgenc
authors.forename: Edward S
authors.initials: ES
authors.lastname: Szekeres
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Lawrence
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D004265:DNA Helicases / Q000235:genetics* / Q000378:metabolism; D004257:DNA Polymerase II / Q000378:metabolism; D004261:DNA Replication / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004706:Endodeoxyribonucleases / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics* / Q000528:radiation effects; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D005090:Exodeoxyribonucleases / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D039002:Prophages / Q000235:genetics; D011995:Recombination, Genetic / Q000235:genetics*; D014466:Ultraviolet Rays
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C084497:RecT protein, E coli; C061260:RuvB protein, Bacteria; C489340:recF protein, E coli; C069806:ruvC protein, E coli; C071446:RecG protein, E coli; D004257:DNA Polymerase II; D004706:Endodeoxyribonucleases; D005090:Exodeoxyribonucleases; C038225:recE protein, E coli; C071059:Holliday junction DNA helicase, E coli; D000251:Adenosine Triphosphatases; C506743:priA protein, E coli; D004265:DNA Helicases
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