CRYSTALLOGRAPHIC STUDIES OF KU70 & 80

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We have obtained small crystals of Ku70/80, a complex of Ku70 and Ku80, bound to DNA and bound to ATP. The two proteins Ku70 and K80 together form the regulatory component of DNA-dependent protein kinase (DNA-PK), a 460 kD protein that responds to DNA damage. The Ku70/80 complex binds to double-stranded breaks and to double-stranded-to-single-stranded transitions. Once bound, the Ku70/80 complex recruits the catalytic subunit of DNA-PK. Mutations in either Ku70/80 or in the catalytic subunit result in defects in repair of double-stranded DNA breaks. We plan to bring our crystals to beamline 7-1 to assess their quality. The principal reason this experiment has to be done at a synchrotron is that the crystals are extremely small -- the largest are 0.1 x 0.1 x 0.1 mm. The crystals appear cubic. Diffraction from these crystals can barely be detected at our home source. We anticipate that the unit cell will have dimensions on the order of 300-400 E.