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      Pathways of DNA Double-Strand Break Repair during the Mammalian Cell Cycle

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          Abstract

          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 gamma-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 G(1), greater impairment in S, and a substantial defect in late S/G(2). Furthermore, the radiosensitivity of irs1SF cells is slight in G(1) but dramatically higher in late S/G(2), 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/G(2), 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.

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          Author and article information

          Journal
          Molecular and Cellular Biology
          Molecular and Cellular Biology
          American Society for Microbiology
          0270-7306
          August 15 2003
          July 31 2003
          August 15 2003
          : 23
          : 16
          : 5706-5715
          Article
          10.1128/MCB.23.16.5706-5715.2003
          166351
          12897142
          a8cfd6ea-3694-427b-ba3e-855e12de6a75
          © 2003
          History

          Molecular medicine,Neurosciences
          Molecular medicine, Neurosciences

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