title: An exonuclease I-sensitive DNA repair pathway in Deinococcus radiodurans: a major determinant of radiation resistance.
abstract: Deinococcus radiodurans R1 recovering from acute dose of gamma radiation shows a biphasic mechanism of DNA double-strand break repair. The possible involvement of microsequence homology-dependent, or non-homologous end joining type mechanisms during initial period followed by RecA-dependent homologous recombination pathways has been suggested for the reconstruction of complete genomes in this microbe. We have exploited the known roles of exonuclease I in DNA recombination to elucidate the nature of recombination involved in DNA double-strand break repair during post-irradiation recovery of D. radiodurans. Transgenic Deinococcus cells expressing exonuclease I functions of Escherichia coli showed significant reduction in gamma radiation radioresistance, while the resistance to far-UV and hydrogen peroxide remained unaffected. The overexpression of E. coli exonuclease I in Deinococcus inhibited DNA double-strand break repair. Such cells exhibited normal post-irradiation expression kinetics of RecA, PprA and single-stranded DNA-binding proteins but lacked the divalent cation manganese [(Mn(II)]-dependent protection from gamma radiation. The results strongly suggest that 3' (rho) 5' single-stranded DNA ends constitute an important component in recombination pathway involved in DNA double-strand break repair and that absence of sbcB from deinococcal genome may significantly aid its extreme radioresistance phenotype.
authors.affiliation: Molecular Biology Division, Bhabha Atomic Research Centre, Mumbai- 400 085, India. hsmisra@barc.ernet.in
authors.forename: Hari S
authors.initials: HS
authors.lastname: Misra
authors.forename: Nivedita P
authors.initials: NP
authors.lastname: Khairnar
authors.forename: Swathi
authors.initials: S
authors.lastname: Kota
authors.forename: Smriti
authors.initials: S
authors.lastname: Shrivastava
authors.forename: Vasudha P
authors.initials: VP
authors.lastname: Joshi
authors.forename: Shree K
authors.initials: SK
authors.lastname: Apte
mesh_terms: D004260:DNA Repair / Q000235:genetics; D004269:DNA, Bacterial / Q000378:metabolism / Q000528:radiation effects; D004277:DNA, Single-Stranded / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology; D034301:Deinococcus / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000502:physiology; D005090:Exodeoxyribonucleases / Q000235:genetics* / Q000502:physiology*; D005720:Gamma Rays; D008345:Manganese / Q000494:pharmacology; D008969:Molecular Sequence Data; D011836:Radiation Tolerance / Q000235:genetics*; D011938:Rec A Recombinases / Q000235:genetics / Q000502:physiology; D011995:Recombination, Genetic / Q000235:genetics
chemical_list: D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D008345:Manganese; D011938:Rec A Recombinases; D005090:Exodeoxyribonucleases; C028450:exodeoxyribonuclease I