The repair of DNA methylation damage in Saccharomyces cerevisiae.
The major genotoxicity of methyl methanesulfonate (MMS) is due to the production of a lethal 3-methyladenine (3MeA) lesion. An alkylation-specific base-excision repair pathway in yeast is initiated by a Mag1 3MeA DNA glycosylase that removes the damaged base, followed by an Apn1 apurinic/ apyrimidinic endonuclease that cleaves the DNA strand at the abasic site for subsequent repair. MMS is also regarded as a radiomimetic agent, since a number of DNA radiation-repair mutants are also sensitive to MMS. To understand how these radiation-repair genes are involved in DNA methylation repair, we performed an epistatic analysis by combining yeast mag1 and apn1 mutations with mutations involved in each of the RAD3, RAD6 and RAD52 groups. We found that cells carrying rad6, rad18, rad50 and rad52 single mutations are far more sensitive to killing by MMS than the mag1 mutant, that double mutants were much more sensitive than either of the corresponding single mutants, and that the effects of the double mutants were either additive or synergistic, suggesting that post-replication and recombination-repair pathways recognize either the same lesions as MAG1 and APN1, or else some differ- ent lesions produced by MMS treatment. Lesions handled by recombination and post replication repair are not simply 3MeA, since over-expression of the MAG1 gene does not offset the loss of these pathways. Based on the above analyses, we discuss possible mechanisms for the repair of methylation damage by various pathways.
Xiao
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Department of Microbiology, University of Saskatchewan, Saskatoon, SK, S7N 5E5, Canada.
Chow
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BL
Rathgeber
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D000251:Adenosine Triphosphatases / Q000235:genetics; D000478:Alkylation; D045647:DNA Glycosylases; D004265:DNA Helicases / Q000235:genetics; D019175:DNA Methylation; D004260:DNA Repair; D004271:DNA, Fungal / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics; D005800:Genes, Fungal; D008025:Ligases / Q000235:genetics; D008741:Methyl Methanesulfonate / Q000494:pharmacology; D009154:Mutation; D009699:N-Glycosyl Hydrolases / Q000235:genetics; D051721:Rad52 DNA Repair and Recombination Protein; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D044763:Ubiquitin-Conjugating Enzymes
D004271:DNA, Fungal; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C497197:RAD52 protein, S cerevisiae; D051721:Rad52 DNA Repair and Recombination Protein; D029701:Saccharomyces cerevisiae Proteins; D008741:Methyl Methanesulfonate; C471606:RAD6 protein, S cerevisiae; D044763:Ubiquitin-Conjugating Enzymes; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; D000251:Adenosine Triphosphatases; C061897:Rad3 protein, S cerevisiae; D004265:DNA Helicases; D008025:Ligases