TY - JOUR
T1 - A Possible Role of Ku in Mediating Sequential Repair of Closely Opposed Lesions
AU - Hashimoto, Mitsumasa
AU - Donald, Carlton D.
AU - Yannone, Steven M.
AU - Chen, David J.
AU - Roy, Robindra
AU - Kow, Yoke W.
PY - 2001/4/20
Y1 - 2001/4/20
N2 - One of the hallmarks of ionizing radiation exposure is the formation of clustered damage that includes closely opposed lesions. We show that the Ku70/ 80 complex (Ku) has a role in the repair of closely opposed lesions in DNA. DNA containing a dihydrouracil (DHU) close to an opposing single strand break was used as a model substrate. It was found that Ku has no effect on the enzymatic activity of human endonuclease III when the substrate DNA contains only DHU. However, with DNA containing a DHU that is closely opposed to a single strand break, Ku inhibited the nicking activity of human endonuclease III as well as the amount of free double strand breaks induced by the enzyme. The inhibition on the formation of a free double strand break by Ku was found to be much greater than the inhibition of human endonuclease III-nicking activity by Ku. Furthermore, there was a concomitant increase in the formation of Ku-DNA complexes when endonuclease III was present. Similar results were also observed with Escherichia coli endonuclease III. These results suggest that Ku reduces the formation of endonuclease III-induced free double strand breaks by sequestering the double strand breaks formed as a KU-DNA complex. In doing so, Ku helps to avoid the formation of the intermediary free double strand breaks, possibly helping to reduce the mutagenic event that might result from the misjoining of frank double strand breaks.
AB - One of the hallmarks of ionizing radiation exposure is the formation of clustered damage that includes closely opposed lesions. We show that the Ku70/ 80 complex (Ku) has a role in the repair of closely opposed lesions in DNA. DNA containing a dihydrouracil (DHU) close to an opposing single strand break was used as a model substrate. It was found that Ku has no effect on the enzymatic activity of human endonuclease III when the substrate DNA contains only DHU. However, with DNA containing a DHU that is closely opposed to a single strand break, Ku inhibited the nicking activity of human endonuclease III as well as the amount of free double strand breaks induced by the enzyme. The inhibition on the formation of a free double strand break by Ku was found to be much greater than the inhibition of human endonuclease III-nicking activity by Ku. Furthermore, there was a concomitant increase in the formation of Ku-DNA complexes when endonuclease III was present. Similar results were also observed with Escherichia coli endonuclease III. These results suggest that Ku reduces the formation of endonuclease III-induced free double strand breaks by sequestering the double strand breaks formed as a KU-DNA complex. In doing so, Ku helps to avoid the formation of the intermediary free double strand breaks, possibly helping to reduce the mutagenic event that might result from the misjoining of frank double strand breaks.
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U2 - 10.1074/jbc.M010906200
DO - 10.1074/jbc.M010906200
M3 - Article
C2 - 11278783
AN - SCOPUS:0035918156
SN - 0021-9258
VL - 276
SP - 12827
EP - 12831
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 16
ER -