title: Distinct pathways of nonhomologous end joining that are differentially regulated by DNA-dependent protein kinase-mediated phosphorylation.
abstract: Nonhomologous end joining is the most common mechanism of DNA double-strand break repair in human cells. Here we show that nonhomologous end joining can occur by two biochemically distinct pathways. One requires a fraction containing the Mre11-Rad50-NBS1 complex. The other requires a fraction containing a novel, approximately 200-kDa factor that does not correspond to any of the previously described double-strand break repair proteins. The two pathways converge, sharing a common requirement for the DNA ligase IV-XRCC4 complex to catalyze the final step of phosphodiester bond formation. Whereas the Mre11-Rad50-NBS1-dependent pathway does not require, and may be inhibited by, DNA-dependent protein kinase-mediated phosphorylation, the new pathway depends on this phosphorylation for release from a DNA-dependent protein kinase-mediated reaction checkpoint. The existence of two distinct pathways, which are differentially regulated by the DNA-dependent protein kinase, provides a possible explanation for the selective repair defects seen in DNA-dependent protein kinase-deficient mutants.
authors.affiliation: Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta, GA 30912, USA.
authors.forename: Durga
authors.initials: D
authors.lastname: Udayakumar
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Bladen
authors.forename: Farlyn Z
authors.initials: FZ
authors.lastname: Hudson
authors.forename: William S
authors.initials: WS
authors.lastname: Dynan
mesh_terms: D017766:Acid Anhydride Hydrolases; D018797:Cell Cycle Proteins / Q000378:metabolism; D002847:Chromatography, Agarose; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000378:metabolism; D004260:DNA Repair; D045643:DNA Repair Enzymes; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D000076228:MRE11 Homologue Protein; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism* / Q000502:physiology*
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C000607893:LIG4 protein, human; C121766:MRE11 protein, human; C112156:NBN protein, human; D009687:Nuclear Proteins; C101467:XRCC4 protein, human; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases; D000076228:MRE11 Homologue Protein; D017766:Acid Anhydride Hydrolases; C112158:RAD50 protein, human; D011088:DNA Ligases; D045643:DNA Repair Enzymes; D000072481:DNA Ligase ATP