title: Methyl methanesulfonate (MMS) produces heat-labile DNA damage but no detectable in vivo DNA double-strand breaks.
abstract: Homologous recombination (HR) deficient cells are sensitive to methyl methanesulfonate (MMS). HR is usually involved in the repair of DNA double-strand breaks (DSBs) in Saccharomyces cerevisiae implying that MMS somehow induces DSBs in vivo. Indeed there is evidence, based on pulsed-field gel electrophoresis (PFGE), that MMS causes DNA fragmentation. However, the mechanism through which MMS induces DSBs has not been demonstrated. Here, we show that DNA fragmentation following MMS treatment, and detected by PFGE is not the consequence of production of cellular DSBs. Instead, DSBs seen following MMS treatment are produced during sample preparation where heat-labile methylated DNA is converted into DSBs. Furthermore, we show that the repair of MMS-induced heat-labile damage requires the base excision repair protein XRCC1, and is independent of HR in both S.cerevisiae and mammalian cells. We speculate that the reason for recombination-deficient cells being sensitive to MMS is due to the role of HR in repair of MMS-induced stalled replication forks, rather than for repair of cellular DSBs or heat-labile damage.
authors: Department of Genetics, Microbiology and Toxicology, Stockholm University Svante Arrhenius väg 16, S-106 91 Stockholm, Sweden.
authors: Cecilia
authors: C
authors: Lundin
authors: Matthew
authors: M
authors: North
authors: Klaus
authors: K
authors: Erixon
authors: Kevin
authors: K
authors: Walters
authors: Dag
authors: D
authors: Jenssen
authors: Alastair S H
authors: AS
authors: Goldman
authors: Thomas
authors: T
authors: Helleday
mesh_terms: D000477:Alkylating Agents / Q000633:toxicity*; D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D004249:DNA Damage; D004260:DNA Repair; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000502:physiology; D016521:Electrophoresis, Gel, Pulsed-Field; D006358:Hot Temperature; D008741:Methyl Methanesulfonate / Q000633:toxicity*; D008769:Methylnitronitrosoguanidine / Q000633:toxicity; D011995:Recombination, Genetic; D000076105:X-ray Repair Cross Complementing Protein 1; D015003:Yeasts / Q000187:drug effects / Q000235:genetics
chemical_list: D000477:Alkylating Agents; D004268:DNA-Binding Proteins; D000076105:X-ray Repair Cross Complementing Protein 1; D008769:Methylnitronitrosoguanidine; D008741:Methyl Methanesulfonate