Identification and preliminary characterization of an O super(6)-methylguanine DNA repair methyltransferase in the yeast Saccharomyces cerevisiae

Saccharomyces cerevisiae contains a DNA repair methyltransferase (MTase) that repairs O super(6)-methylguanine. Methyl groups are irreversibly transferred from O super(6)-methylguanine in DNA to a 25-kilodalton protein in S. cerevisiae) cell extracts, and methyl transfer is accompanied by the formation of S-methylcysteine. The yeast MTase is expressed at approximately 150 molecules/cell in exponentially growing yeast cultures but is not detectable in stationary phase cells. Unlike mammalian and bacterial MTases, the yeast MTase is very temperature-sensitive, having a half-life of about 4 min at 37 degree C, which may explain why others have failed to detect it. Like other DNA repair MTases, the S. cerevisiae MTase repairs O super(6)-methylguanine more efficiently in double-stranded DNA than in single-stranded DNA.