title: Coordinate action of the helicase and 3' to 5' exonuclease of Werner syndrome protein.
abstract: Werner syndrome is a human disorder characterized by premature aging, genomic instability, and abnormal telomere metabolism. The Werner syndrome protein (WRN) is the only known member of the RecQ DNA helicase family that contains a 3' --> 5'-exonuclease. However, it is not known whether both activities coordinate in a biological pathway. Here, we describe DNA structures, forked duplexes containing telomeric repeats, that are substrates for the simultaneous action of both WRN activities. We used these substrates to study the interactions between the WRN helicase and exonuclease on a single DNA molecule. WRN helicase unwinds at the forked end of the substrate, whereas the WRN exonuclease acts at the blunt end. Progression of the WRN exonuclease is inhibited by the action of WRN helicase converting duplex DNA to single strand DNA on forks of various duplex lengths. The WRN helicase and exonuclease act in concert to remove a DNA strand from a long forked duplex that is not completely unwound by the helicase. We analyzed the simultaneous action of WRN activities on the long forked duplex in the presence of the WRN protein partners, replication protein A (RPA), and the Ku70/80 heterodimer. RPA stimulated the WRN helicase, whereas Ku stimulated the WRN exonuclease. In the presence of both RPA and Ku, the WRN helicase activity dominated the exonuclease activity.
authors.affiliation: Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, Maryland 21224, USA.
authors.forename: P L
authors.initials: PL
authors.lastname: Opresko
authors.forename: J P
authors.initials: JP
authors.lastname: Laine
authors.forename: R M
authors.initials: RM
authors.lastname: Brosh
authors.forename: M M
authors.initials: MM
authors.lastname: Seidman
authors.forename: V A
authors.initials: VA
authors.lastname: Bohr
mesh_terms: D034961:Antigens, Nuclear; D001483:Base Sequence; D002384:Catalysis; D004247:DNA / Q000378:metabolism; D004265:DNA Helicases / Q000737:chemistry* / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D043211:Exodeoxyribonuclease V; D005090:Exodeoxyribonucleases / Q000378:metabolism* / Q000502:physiology*; D005092:Exonucleases / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D000072200:Ku Autoantigen; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D012313:RNA / Q000378:metabolism; D053484:RecQ Helicases; D011994:Recombinant Proteins / Q000378:metabolism; D016615:Telomere / Q000378:metabolism; D013997:Time Factors; D014898:Werner Syndrome / Q000378:metabolism*; D000071657:Werner Syndrome Helicase
chemical_list: D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011994:Recombinant Proteins; D012313:RNA; D004247:DNA; D005090:Exodeoxyribonucleases; D005092:Exonucleases; D043211:Exodeoxyribonuclease V; 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