E3 ubiquitin-protein ligase. Participates in CpG methylation-dependent transcriptional regulation and epigenetic transcriptional silencing. Mediates ubiquitination with the E2 ubiquitin-conjugating enzyme UBC11. Promotes methylation-mediated gene silencing leading, for example, to early flowering. Associates with methylated DNA, and can bind to CpG, CpNpG, and CpNpN DNA motifs, with a strong preference for methylated forms, and with highest affinity for CpG substrate. Probably acts at the DNA methylation?histone interface to maintain centromeric heterochromatin. 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. Interacts with histones CENH3, HTB2, HTR3 and H4. Broadly distributed in the nucleus and enriched in the heterochromatic chromocenters. Mostly expressed in inflorescence and, to a lower extent, in leaves. The RING fingers are required for ubiquitin ligase activity. The YDG domain mediates the interaction with histone H3. Centromere DNA hypomethylation and centromeric heterochromatin decondensation in interphase. Decreased DNA methylation primarily at CpG sites in genic regions, as well as repeated sequences in heterochromatic regions. Released transcriptional silencing at heterochromatin regions. Ectopic CpHpH methylation in the 5S rRNA genes against a background of CpG hypomethylation. ORTH2 is missing in cv. Bor-4 that exhibit a centromere repeat hypomethylation phenotype.