Characterization of a novel 8-oxoguanine-DNA glycosylase activity in Escherichia coli and identification of the enzyme as endonuclease VIII.

8-Oxoguanine (G*), induced by reactive oxygen species, is mutagenic because it mispairs with A. The major G*-DNA glycosylase (OGG), namely, OGG1 in eukaryotes, or MutM in Escherichia coli, excises G* when paired in DNA with C, G, and T, but not A, presumably because removal of G* from a G*.A pair would be mutagenic. However, repair of G* will prevent mutation when it is incorporated in the nascent strand opposite A. This could be carried out by a second OGG, OGG2, identified in yeast and human cells. We have characterized a new OGG activity in E. coli and then identified it to be endonuclease VIII (Nei), discovered as a damaged pyrimidine-specific DNA glycosylase. Nei shares sequence homology and reaction mechanism with MutM and is similar to human OGG2 in being able to excise G* when paired with A (or G). Kinetic analysis of wild type Nei showed that it has significant activity for excising G* relative to dihydrouracil. The presence of OGG2 type enzyme in both E. coli and eukaryotes, which is at least as efficient in excising G* from a G*.A (or G) pair as from a G*.C pair, supports the possibility of G* repair in the nascent DNA strand.