Figure 3.

Initiation of DNA demethylation at a CpG site. In adult somatic cells, DNA methylation typically occurs in the context of CpG dinucleotides (CpG sites), forming 5-methylcytosine-pG, or 5mCpG. Reactive oxygen species (ROS) may attack guanine at the dinucleotide site, forming 8-hydroxy-2’-deoxyguanosine (8-OHdG) and resulting in a 5mCp-8-OHdG dinucleotide site. The base excision repair enzyme OGG1 targets 8-OHdG and binds to the lesion without immediate excision. OGG1 present at a 5mCp-8-OHdG site recruits TET1, and TET1 oxidizes the 5mC adjacent to the 8-OHdG. This initiates demethylation of 5mC. (A color version of this figure is available in the online journal.)

Source: Bernstein0275, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0.