title: Interactions of the DNA ligase IV-XRCC4 complex with DNA ends and the DNA-dependent protein kinase.
abstract: The DNA-dependent protein kinase (DNA-PK), consisting of Ku and the DNA-PK catalytic subunit (DNA-PKcs), and the DNA ligase IV-XRCC4 complex function together in the repair of DNA double-strand breaks by non-homologous end joining. These protein complexes are also required for the completion of V(D)J recombination events in immune cells. Here we demonstrate that the DNA ligase IV-XRCC4 complex binds specifically to the ends of duplex DNA molecules and can act as a bridging factor, linking together duplex DNA molecules with complementary but non-ligatable ends. Although the DNA end-binding protein Ku inhibited DNA joining by DNA ligase IV-XRCC4, it did not prevent this complex from binding to DNA. Instead, DNA ligase IV-XRCC4 and Ku bound simultaneously to the ends of duplex DNA molecules. DNA ligase IV-XRCC4 and DNA-PKcs also formed complexes at the ends of DNA molecules, but DNA-PKcs did not inhibit ligation. Interestingly, DNA-PKcs stimulated intermolecular ligation by DNA ligase IV-XRCC4. In the presence of DNA-PK, the majority of the joining events catalyzed by DNA ligase IV-XRCC4 were intermolecular because Ku inhibited intramolecular ligation, but DNA-PKcs still stimulated intramolecular ligation. We suggest that DNA-PKcs-containing complexes formed at DNA ends enhance the association of DNA ends via protein-protein interactions, thereby stimulating intermolecular ligation.
authors.affiliation: Department of Molecular Medicine, Institute of Biotechnology, University of Texas Health Science Center, San Antonio, Texas 78245, USA.
authors.forename: L
authors.initials: L
authors.lastname: Chen
authors.forename: K
authors.initials: K
authors.lastname: Trujillo
authors.forename: P
authors.initials: P
authors.lastname: Sung
authors.forename: A E
authors.initials: AE
authors.lastname: Tomkinson
mesh_terms: D000818:Animals; D002384:Catalysis; D002460:Cell Line; D004247:DNA / Q000378:metabolism*; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000378:metabolism*; D004260:DNA Repair; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D018411:Spodoptera
chemical_list: D004268:DNA-Binding Proteins; C000607893:LIG4 protein, human; D046911:Macromolecular Substances; D009687:Nuclear Proteins; C101467:XRCC4 protein, human; D004247:DNA; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases; D011088:DNA Ligases; D000072481:DNA Ligase ATP