E3 ubiquitin-protein ligase. May participate in CpG methylation-dependent transcriptional regulation (By similarity). S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. The RING fingers are required for ubiquitin ligase activity. The YDG domain mediates the interaction with histone H3.