An exonuclease I-sensitive DNA repair pathway in Deinococcus radiodurans: a major determinant of radiation resistance

Mol Microbiol. 2006 Feb;59(4):1308-16. doi: 10.1111/j.1365-2958.2005.05005.x.


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.

MeSH terms

  • DNA Repair / genetics
  • DNA, Bacterial / metabolism
  • DNA, Bacterial / radiation effects
  • DNA, Single-Stranded / metabolism
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / physiology
  • Deinococcus / enzymology*
  • Deinococcus / genetics
  • Deinococcus / radiation effects*
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / physiology
  • Exodeoxyribonucleases / genetics*
  • Exodeoxyribonucleases / physiology*
  • Gamma Rays
  • Manganese / pharmacology
  • Molecular Sequence Data
  • Radiation Tolerance / genetics*
  • Rec A Recombinases / genetics
  • Rec A Recombinases / physiology
  • Recombination, Genetic / genetics


  • DNA, Bacterial
  • DNA, Single-Stranded
  • DNA-Binding Proteins
  • Escherichia coli Proteins
  • Manganese
  • Rec A Recombinases
  • Exodeoxyribonucleases
  • exodeoxyribonuclease I

Associated data

  • RefSeq/NC_001263