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. {ECO:0000269|PubMed:17239600; ECO:0000269|PubMed:17242155; ECO:0000269|PubMed:18643997; ECO:0000269|PubMed:18704160}.