Homologous recombination and non-homologous end-joining pathways of DNA double-strand break repair have overlapping roles in the maintenance of chromosomal integrity in vertebrate cells

EMBO J. 1998 Sep 15;17(18):5497-508. doi: 10.1093/emboj/17.18.5497.


Eukaryotic cells repair DNA double-strand breaks (DSBs) by at least two pathways, homologous recombination (HR) and non-homologous end-joining (NHEJ). Rad54 participates in the first recombinational repair pathway while Ku proteins are involved in NHEJ. To investigate the distinctive as well as redundant roles of these two repair pathways, we analyzed the mutants RAD54(-/-), KU70(-/-) and RAD54(-/-)/KU70(-/-), generated from the chicken B-cell line DT40. We found that the NHEJ pathway plays a dominant role in repairing gamma-radiation-induced DSBs during G1-early S phase while recombinational repair is preferentially used in late S-G2 phase. RAD54(-/-)/KU70(-/-) cells were profoundly more sensitive to gamma-rays than either single mutant, indicating that the two repair pathways are complementary. Spontaneous chromosomal aberrations and cell death were observed in both RAD54(-/-) and RAD54(-/-)/KU70(-/-) cells, with RAD54(-/-)/KU70(-/-) cells exhibiting significantly higher levels of chromosomal aberrations than RAD54(-/-) cells. These observations provide the first genetic evidence that both repair pathways play a role in maintaining chromosomal DNA during the cell cycle.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Antigens, Nuclear*
  • B-Lymphocytes / cytology
  • B-Lymphocytes / radiation effects
  • Cell Death
  • Cell Line
  • Chickens
  • Chromosome Aberrations*
  • Cloning, Molecular
  • DNA Helicases*
  • DNA Repair / genetics*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / physiology
  • Gamma Rays
  • Interphase
  • Ku Autoantigen
  • Molecular Sequence Data
  • Nuclear Proteins / genetics
  • Nuclear Proteins / physiology
  • Radiation Tolerance
  • Recombination, Genetic / genetics*
  • Sequence Homology, Amino Acid


  • Antigens, Nuclear
  • DNA-Binding Proteins
  • Nuclear Proteins
  • DNA Helicases
  • XRCC5 protein, human
  • Xrcc6 protein, human
  • Ku Autoantigen

Associated data

  • GENBANK/AB016529