title: Geometry of a complex formed by double strand break repair proteins at a single DNA end: recruitment of DNA-PKcs induces inward translocation of Ku protein.
abstract: Ku protein and the DNA-dependent protein kinase catalytic subunit (DNA-PKcs) are essential components of the double-strand break repair machinery in higher eukaryotic cells. Ku protein binds to broken DNA ends and recruits DNA-PKcs to form an enzymatically active complex. To characterize the arrangement of proteins in this complex, we developed a set of photocross-linking probes, each with a single free end. We have previously used this approach to characterize the contacts in an initial Ku-DNA complex, and we have now applied the same technology to define the events that occur when Ku recruits DNA-PKcs. The new probes allow the binding of one molecule of Ku protein and one molecule of DNA-PKcs in a defined position and orientation. Photocross-linking reveals that DNA-PKcs makes direct contact with the DNA termini, occupying an approximately 10 bp region proximal to the free end. Characterization of the Ku protein cross-linking pattern in the presence and absence of DNA-PKcs suggests that Ku binds to form an initial complex at the DNA ends, and that recruitment of DNA-PKcs induces an inward translocation of this Ku molecule by about one helical turn. The presence of ATP had no effect on protein-DNA contacts, suggesting that neither DNA-PK-mediated phosphorylation nor a putative Ku helicase activity plays a role in modulating protein conformation under the conditions tested.
authors.affiliation: Program in Gene Regulation, Institute of Molecular Medicine and Genetics, Medical College of Georgia, 1120 15th Street, Augusta, GA 30912, USA.
authors.forename: S
authors.initials: S
authors.lastname: Yoo
authors.forename: W S
authors.initials: WS
authors.lastname: Dynan
mesh_terms: D034961:Antigens, Nuclear; D001483:Base Sequence; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism; D003432:Cross-Linking Reagents; D004247:DNA / Q000737:chemistry* / Q000378:metabolism*; D004249:DNA Damage; D004265:DNA Helicases; D015342:DNA Probes / Q000737:chemistry; D004260:DNA Repair; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D000072200:Ku Autoantigen; D008958:Models, Molecular; D009687:Nuclear Proteins / Q000737:chemistry* / Q000378:metabolism*; D009690:Nucleic Acid Conformation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry* / Q000378:metabolism*; D020836:Protein Structure, Quaternary
chemical_list: D034961:Antigens, Nuclear; D003432:Cross-Linking Reagents; D015342:DNA Probes; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D004247:DNA; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen