title: Delineation of WRN helicase function with EXO1 in the replicational stress response.
abstract: The WRN gene defective in the premature aging disorder Werner syndrome encodes a helicase/exonuclease. We examined the ability of WRN to rescue DNA damage sensitivity of a yeast mutant defective in the Rad50 subunit of Mre11-Rad50-Xrs2 nuclease complex implicated in homologous recombination repair. Genetic studies revealed WRN operates in a yEXO1-dependent pathway to rescue rad50 sensitivity to methylmethane sulfonate (MMS). WRN helicase, but not exonuclease, is required for MMS resistance. WRN missense mutations in helicase or RecQ C-terminal domains interfered with the ability of WRN to rescue rad50 MMS sensitivity. WRN does not rescue rad50 ionizing radiation (IR) sensitivity, suggesting that WRN, in collaboration with yEXO1, is tailored to relieve replicational stress imposed by alkylated base damage. WRN and yEXO1 are associated with each other in vivo. Purified WRN stimulates hEXO1 nuclease activity on DNA substrates associated with a stalled or regressed replication fork. We propose WRN helicase operates in an EXO1-dependent pathway to help cells survive replicational stress. In contrast to WRN, BLM helicase defective in Bloom's syndrome failed to rescue rad50 MMS sensitivity, but partially restored IR resistance, suggesting a delineation of function by the human RecQ helicases.
authors.affiliation: National Institute on Aging, NIH, NIH Biomedical Research Center, Baltimore, MD 21224, USA.
authors.forename: Monika
authors.initials: M
authors.lastname: Aggarwal
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Sommers
authors.forename: Christa
authors.initials: C
authors.lastname: Morris
authors.forename: Robert M
authors.initials: RM
authors.lastname: Brosh
mesh_terms: D004260:DNA Repair / Q000235:genetics; D045643:DNA Repair Enzymes / Q000235:genetics / Q000502:physiology*; D004261:DNA Replication / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics; D025141:Drug Resistance, Fungal / Q000235:genetics; D005090:Exodeoxyribonucleases / Q000235:genetics / Q000502:physiology*; D005816:Genetic Complementation Test; D006801:Humans; D008741:Methyl Methanesulfonate / Q000494:pharmacology; D053484:RecQ Helicases / Q000235:genetics / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics; D013312:Stress, Physiological / Q000235:genetics*; D000071657:Werner Syndrome Helicase
chemical_list: D004268:DNA-Binding Proteins; C086930:RAD50 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D008741:Methyl Methanesulfonate; C114331:EXO1 protein, human; D005090:Exodeoxyribonucleases; D053484:RecQ Helicases; C098785:WRN protein, human; D000071657:Werner Syndrome Helicase; D045643:DNA Repair Enzymes
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