Efficient and accurate replication in the presence of 7,8-dihydro-8-oxoguanine by DNA polymerase eta

Oxidative damage to DNA has been proposed to have a role in cancer and agei ng(1). Oxygen-free radicals formed during normal aerobic cellular metabolis m attack bases in DNA, and 7,8-dihydro-8-oxoguanine (8-oxoG) is one of the adducts formed(2,3). Eukaryotic replicative DNA polymerases replicate DNA c ontaining 8-oxoG by inserting an adenine opposite the lesion(4); consequent ly. 8-oxoG is highly mutagenic and causes G:C to T:A transversions(5). Gene tic studies in yeast have indicated a role for mismatch repair in minimizin g the incidence of these mutations. In Saccharomyces cerevisiae, deletion o f OGG1, encoding a DNA glycosylase that functions in the removal of 8-oxoG when paired with C, causes an increase in the rate of G:C to TA transversio ns(6). The ogg1 Delta msh2 Delta double mutant displays a higher rate of CA N1(S) to can1(r) forward mutations than the ogg1 Delta or msh2 Delta single mutants, and this enhanced mutagenesis is primarily due to C:C to T:A tran sversions(7). The gene RAD30 of S. cerevisiae encodes a DNA polymerase, Pol eta, that efficiently replicates DNA containing a cis-syn thymine-thymine (T-T) dimer by inserting two adenines across from the dimers. In humans, mu tations in the yeast RAD30 counterpart, POLH, cause the variant form of xer oderma pigmentosum(9,10) (XP-V), and XP-V individuals suffer from a high in cidence of sunlight-induced skin cancers. Here we show that yeast and human POL eta replicate DNA containing 8-oxoG efficiently and accurately by inse rting a cytosine across from the lesion and by proficiently extending from this base pair. Consistent with these biochemical studies, a synergistic in crease in the rate of spontaneous mutations occurs in the absence of POL et a in the yeast ogg1 Delta mutant. Our results suggest an additional role fo r Pol eta in the prevention of internal cancers in humans that would otherw ise result from the mutagenic replication of 8-oxoG in DNA.