DNA-dependent protein kinase (Ku protein-p350 complex) assembles on double-stranded DNA.
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The Ku protein is an autoantigen that consists of 70- and 80-kDa polypeptides. It associates with double-stranded DNA at free ends. In the present study, we examined the ability of anti-Ku antibodies to immunoprecipitate various structures from extracts of HeLa cells prepared at different salt concentrations. Under physiological conditions, these antibodies identified a complex containing the Ku protein and the 350-kDa component (p350) of DNA-dependent protein kinase (DNA-PK), which appeared to be closely associated on the DNA strand. In reconstitution experiments with cell extracts and biochemically purified components, the Ku protein-p350 complex formed only in the presence of double-stranded DNA. The reconstituted complex was catalytically active. Together with previous studies, these results indicate that the Ku protein interacts with DNA to create a binding site for p350 as the DNA-PK holoenzyme assembles. IMAGES:
