Methyl methanesulfonate (MMS) produces heat-labile DNA damage but no detectable in vivo DNA double-strand breaks.
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.
Lundin
Cecilia
C
Department of Genetics, Microbiology and Toxicology, Stockholm University Svante Arrhenius väg 16, S-106 91 Stockholm, Sweden.
North
Matthew
M
Erixon
Klaus
K
Walters
Kevin
K
Jenssen
Dag
D
Goldman
Alastair S H
AS
Helleday
Thomas
T
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
D000477:Alkylating Agents; D004268:DNA-Binding Proteins; D000076105:X-ray Repair Cross Complementing Protein 1; D008769:Methylnitronitrosoguanidine; D008741:Methyl Methanesulfonate