title: Human Ku70/80 protein blocks exonuclease 1-mediated DNA resection in the presence of human Mre11 or Mre11/Rad50 protein complex.
abstract: DNA double strand breaks (DSB) are repaired by nonhomologous end-joining (NHEJ) or homologous recombination (HR). Recent genetic data in yeast shows that the choice between these two pathways for the repair of DSBs is via competition between the NHEJ protein, Ku, and the HR protein, Mre11/Rad50/Xrs2 (MRX) complex. To study the interrelationship between human Ku and Mre11 or Mre11/Rad50 (MR), we established an in vitro DNA end resection system using a forked model dsDNA substrate and purified human Ku70/80, Mre11, Mre11/Rad50, and exonuclease 1 (Exo1). Our study shows that the addition of Ku70/80 blocks Exo1-mediated DNA end resection of the forked dsDNA substrate. Although human Mre11 and MR bind to the forked double strand DNA, they could not compete with Ku for DNA ends or actively mediate the displacement of Ku from the DNA end either physically or via its exonuclease or endonuclease activity. Our in vitro studies show that Ku can block DNA resection and suggest that Ku must be actively displaced for DNA end processing to occur and is more complicated than the competition model established in yeast.
authors.affiliation: Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA.
authors.forename: Jingxin
authors.initials: J
authors.lastname: Sun
authors.forename: Kyung-Jong
authors.initials: KJ
authors.lastname: Lee
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Davis
authors.forename: David J
authors.initials: DJ
authors.lastname: Chen
mesh_terms: D017766:Acid Anhydride Hydrolases; D034961:Antigens, Nuclear / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004247:DNA / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D045643:DNA Repair Enzymes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D005090:Exodeoxyribonucleases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D000072200:Ku Autoantigen; D000076228:MRE11 Homologue Protein; D046912:Multiprotein Complexes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; C121766:MRE11 protein, human; D046912:Multiprotein Complexes; D004247:DNA; C114331:EXO1 protein, human; D005090:Exodeoxyribonucleases; D000076228:MRE11 Homologue Protein; D017766:Acid Anhydride Hydrolases; C112158:RAD50 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen; D045643:DNA Repair Enzymes