The rate of hOGG1-mediated 8-oxoG removal from nucleosomal DNA

When left unrepaired, DNA damage can lead to mutagenesis and carcinogenesis. Organisms have evolved to repair DNA damage through several pathways, including the removal and replacement of damaged DNA bases via base excision repair (BER). This pathway involves an enzymatic cascade: following removal of the damaged base by a glycosylase, the damage site is treated by an apurinic/apyrimidinic lyase, and then patched by a polymerase. Much is known about the BER pathway and the enzymes involved in it (Brooks et al., 2013); however, studies of BER in the context of eukaryotic DNA have only recently begun (Odell, Wallace, & Pederson, 2013). In eukaryotic cells, short stretches (146 base pairs) of genomic DNA are wrapped around octameric clusters of histone proteins, forming macromolecular structures called nucleosomes (Eickbush & Moudrianakis, 1978). The nucleosome presents a particular challenge to BER enzymes: the rate and efficiency of repair at a particular lesion site are expected to depend on the relative rotational and translational position of the lesion site on the histone core. Here, we examine the rate and efficiency of the removal of 8-oxo-7,8-dihydroguanine (8-oxoG), the predominant oxidative lesion in DNA (Michaels & Miller, 1992), by the glycosylase hOGG1 as a function of position within the nucleosome. These results are compared with the rate and efficiency of the hOGG1 reaction on free DNA substrates, which have previously been observed in our laboratory (Jarem, Wilson, & Delaney 2009; Jarem et al., 2011). These experiments will provide a basis for further explorations into the factors affecting the efficiency of BER in eukaryotic DNA.