Saccharomyces cerevisiae 3-methyladenine DNA glycosylase has homology to the AlkA glycosylase of E. coli and is induced in response to DNA alkylation damage.

Abstract

We previously cloned a DNA fragment from Saccharomyces cerevisiae that suppressed the alkylation sensitivity of Escherichia coli glycosylase deficient mutants and we showed that it apparently contained a gene for 3‐methyl‐adenine DNA glycosylase (MAG). Here we establish the identity of the MAG gene by sequence analysis and describe its in vivo function and expression in yeast cells. The MAG DNA glycosylase specifically protects yeast cells against the killing effects of alkylating agents. It does not protect cells against mutation; indeed, it appears to generate mutations which presumably result from those apurinic sites produced by the glycosylase that escape further repair. The MAG gene, which we mapped to chromosome V, is not allelic with any of the RAD genes and appears to be allelic to the unmapped MMS‐5 gene. From its sequence the MAG glycosylase is predicted to contain 296 amino acids and have a molecular weight of 34,293 daltons. A 137 amino acid stretch of the MAG glycosylase displays 27.0% identity and 63.5% similarity with the E. coli AlkA glycosylase. Transcription of the MAG gene, like that of the E. coli alkA gene, is greatly increased when yeast cells are exposed to relatively non‐toxic levels of alkylating agents.

DNA glycosylases in the base excision repair of DNA

“…AlkA is, however, clearly related to the S. cere isiae protein MAG [122][123][124] and to the S. pombe protein Mag1 [125]. In contrast, the single MPG identified in human, rat and murine cells is unrelated to bacterial and yeast glycosylases.…”

“…N-glycosylases that excise alkylated bases have been identified in E. coli (Tag and AlkA), [117][118][119], other bacteria [120,121], Saccharomyces cere isiae (MAG) [122][123][124], Schizosaccharomyces pombe (Mag1) [125], plants [3-meA-DNA glycosylase (MPG)] [126] and mammalian cells (MPG) [127][128][129][130][131][132][133]. These studies have demonstrated that AlkA and yeast glycosylases are related, whereas plant and mammalian alkyl-DNA glycosylases constitute a different family.…”

Contribution of Base Excision Repair, Nucleotide Excision Repair, and DNA Recombination to Alkylation Resistance of the Fission Yeast Schizosaccharomyces pombe

“…MMS doses that had no effect on survival of the wild type allowed less than 0.01% survival of 3MeA DNA glycosylase-deficient E. coli (8). Similarly, in S. cerevisiae, doses of MMS that allowed greater than 10% survival in the wild type allowed less than 0.0001% survival in mag1 S. cerevisiae (9). The contribution of 3MeA DNA glycosylase activity to MMS sensitivity of mammalian cells was more modest but nevertheless significant; MMS doses that allowed approximately 10% survival of the wild type caused less than 1% survival of 3MeA DNA glycosylase-deficient Aag Ϫ/Ϫ null cells (12).…”

Substrate specificity and sequence-dependent activity of the Saccharomyces cerevisiae 3-methyladenine DNA glycosylase (Mag)

“…The budding yeast Saccharomyces cerevisiae, upon exposure to non-lethal levels of alkylating agents, induces the expression of Mag, the 3MeA DNA glycosylase encoded by the MAG gene [10]. Mag shares significant structural and functional homology with the similarly inducible E. coli 3MeA DNA glycosylase, namely AlkA ( Figure 1A).…”