MOLECULAR-CLONING AND FUNCTIONAL EXPRESSION OF A HUMAN CDNA-ENCODING THE ANTIMUTATOR ENZYME 8-HYDROXYGUANINE-DNA GLYCOSYLASE

The major mutagenic base lesion in DNA caused by exposure to reactive oxygen species is 8-hydroxyguanine (8-oxo-7,8-dihydroguanine), In bact eria and Saccharomyces cerevisiae, this damaged base is excised by a D NA glycosylase with an associated lyase activity for chain cleavage. W e have cloned, sequenced, and expressed a human cDNA with partial sequ ence homology to the relevant yeast gene, The encoded 47-kDa human enz yme releases free 8-hydroxyguanine from oxidized DNA and introduces a chain break in a double-stranded oligonucleotide specifically at an 8- hydroxyguanine residue base paired with cytosine, Expression of the hu man protein in a DNA repair-deficient E. coli mutM mutY strain partly suppresses its spontaneous mutator phenotype. The gene encoding the hu man enzyme maps to chromosome 3p25. These results show that human cell s have an enzyme that fan initiate base excision repair at mutagenic D NA lesions caused by active oxygen.