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Mol. Cell. Biol., Mar 1997, 1425-1433, Vol 17, No. 3
SE Lee, RA Mitchell, A Cheng and EA Hendrickson
Mice homozygous for the scid (severe combined immune deficiency) mutation
are defective in the repair of DNA double-strand breaks (DSBs) and are
consequently very X-ray sensitive and defective in the lymphoid V(D)J
recombination process. Recently, a strong candidate for the scid gene has
been identified as the catalytic subunit of the DNA-dependent protein
kinase (DNA-PK) complex. Here, we show that the activity of the DNA-PK
complex is regulated in a cell cycle-dependent manner, with peaks of
activity found at the G1/early S phase and again at the G2 phase in
wild-type cells. Interestingly, only the deficit of the G1/early S phase
DNA-PK activity correlated with an increased hypersensitivity to
X-irradiation and a DNA DSB repair deficit in synchronized scid pre-B
cells. Finally, we demonstrate that the DNA-PK activity found at the G2
phase may be required for exit from a DNA damage-induced G2 checkpoint
arrest. These observations suggest the presence of two pathways
(DNA-PK-dependent and -independent) of illegitimate mammalian DNA DSB
repair and two distinct roles (DNA DSB repair and G2 checkpoint traversal)
for DNA-PK in the cellular response to ionizing radiation.
Copyright © 1997, American Society for Microbiology
Evidence for DNA-PK-dependent and -independent DNA double-strand break repair pathways in mammalian cells as a function of the cell cycle
Department of Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, Rhode Island 02912, USA.
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