Pathways of DNA double-strand break repair during the mammalian cell cycle

Kai Rothkamm, Ines Krüger, Larry H. Thompson, Markus Löbrich

Research output: Contribution to journalArticlepeer-review

909 Scopus citations


Little is known about the quantitative contributions of nonhomologous end joining (NHEJ) and homologous recombination (HR) to DNA double-strand break (DSB) repair in different cell cycle phases after physiologically relevant doses of ionizing radiation. Using immunofluorescence detection of γ-H2AX nuclear foci as a novel approach for monitoring the repair of DSBs, we show here that NHEJ-defective hamster cells (CHO mutant V3 cells) have strongly reduced repair in all cell cycle phases after 1 Gy of irradiation. In contrast, HR-defective CHO irs1SF cells have a minor repair defect in G1, greater impairment in S, and a substantial defect in late S/G2. Furthermore, the radiosensitivity of irs1SF cells is slight in G1 but dramatically higher in late S/G2, while V3 cells show high sensitivity throughout the cell cycle. These findings show that NHEJ is important in all cell cycle phases, while HR is particularly important in late S/G2, where both pathways contribute to repair and radioresistance. In contrast to DSBs produced by ionizing radiation, DSBs produced by the replication inhibitor aphidicolin are repaired entirely by HR. irs1SF, but not V3, cells show hypersensitivity to aphidicolin treatment. These data provide the first evaluation of the cell cycle-specific contributions of NHEJ and HR to the repair of radiation-induced versus replication-associated DSBs.

Original languageEnglish (US)
Pages (from-to)5706-5715
Number of pages10
JournalMolecular and Cellular Biology
Issue number16
StatePublished - Aug 2003
Externally publishedYes

ASJC Scopus subject areas

  • Molecular Biology
  • Genetics
  • Cell Biology


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