title: Requirements for the nucleolytic processing of DNA ends by the Werner syndrome protein-Ku70/80 complex.
abstract: Werner syndrome (WS) is an inherited disease characterized by premature onset of aging, increased cancer incidence, and genomic instability. The WS gene encodes a protein with helicase and exonuclease activities. Our previous studies indicated that the Werner syndrome protein (WRN) interacts with Ku, a heterodimeric factor of 70- and 80-kDa subunits implicated in the repair of double strand DNA breaks. Moreover, we demonstrated that Ku70/80 strongly stimulates and alters WRN exonuclease activity. In this report, we investigate further the association between WRN and Ku70/80. First, using various WRN deletion mutants we show that 50 amino acids at the amino terminus are required and sufficient to interact with Ku70/80. In addition, our data indicate that the region of Ku80 between amino acids 215 and 276 is necessary for binding to WRN. Then, we show that the amino-terminal region of WRN from amino acid 1 to 388, which comprise the exonuclease domain, can be efficiently stimulated by Ku to degrade DNA substrates, indicating that the helicase domain and the carboxyl-terminal tail are not required for the stimulatory process. Finally, using gel shift assays, we demonstrate that Ku recruits WRN to DNA. Taken together, these results suggest that Ku-mediated activation of WRN exonuclease activity may play an important role in a cellular pathway that requires processing of DNA ends.
authors.affiliation: Department of Molecular Microbiology and Immunology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, USA.
authors.forename: B
authors.initials: B
authors.lastname: Li
authors.forename: L
authors.initials: L
authors.lastname: Comai
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D034961:Antigens, Nuclear; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D003001:Cloning, Molecular; D004247:DNA / Q000378:metabolism*; D004265:DNA Helicases / Q000737:chemistry / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005090:Exodeoxyribonucleases; D005092:Exonucleases / Q000378:metabolism; D017353:Gene Deletion; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D007313:Insecta; D000072200:Ku Autoantigen; D009687:Nuclear Proteins / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D053484:RecQ Helicases; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D014898:Werner Syndrome / Q000235:genetics* / Q000378:metabolism; D000071657:Werner Syndrome Helicase
chemical_list: D000596:Amino Acids; D034961:Antigens, Nuclear; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; D004247:DNA; D005982:Glutathione Transferase; D005090:Exodeoxyribonucleases; D005092:Exonucleases; D004265:DNA Helicases; D053484:RecQ Helicases; C098785:WRN protein, human; D000071657:Werner Syndrome Helicase; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen