FORMAMIDOPYRIMIDINE DNA GLYCOSYLASE IN THE YEAST SACCHAROMYCES-CEREVISIAE

A DNA glycosylase that excises 2,6-diamino-4-hydroxy-5N-methylformamid opyrimidine (Fapy) from double stranded DNA has been purified 28,570-f old from the yeast Saccharomyces cerevisiae. Gel filtration chromatogr aphy shows that yeast Fapy DNA glycosylase has a molecular weight of a bout 40 kDa. The Fapy DNA glycosylase is active in the presence of EDT A, but is completely inhibited by 0.2 M KCI. Yeast Fapy DNA glycosylas e does not excise N-7-methylguanine, N-3-methyladenine or uracil. A re pair enzyme for 7,8-dihydro-8-oxoguanine (8-OxoG) co-purifies with the Fapy DNA glycosylase. This repair activity causes strand cleavage at the site of 8-OxoG in DNA duplexes. The highest rate of incision of th e 8-OxoG-containing strand was observed for duplexes where 8-OxoG was opposite guanine. The mode of incision at 8-OxoG was not established y et. The results however suggest that the Fapy- and 8-OxoG-repair activ ities are associated with a single protein.