Acts as transcriptional repressor and plays a role in gene silencing. Does not bind to DNA by itself (PubMed:12124384). Binds to DNA with a preference for sites containing methylated CpG dinucleotides (in vitro). Binds to a lesser degree DNA containing unmethylated CpG dinucleotides (PubMed:24307175). Recruits histone deacetylases and DNA methyltransferases. Heterodimer with MBD2 (PubMed:10947852). Part of the NuRD and the MeCP1 complex (PubMed:12124384, PubMed:11756549, PubMed:15454082). Interacts with BCL6, HDAC1, MTA2, DNMT1, p66-alpha and p66-beta (PubMed:11102443, PubMed:12124384, PubMed:12183469, PubMed:11756549, PubMed:15454082). Does not interact with PWWP2A and PWWP2B (By similarity). Nuclear, in discrete foci. Detected on chromatin, at promoter regions of active genes. Extended N-terminus.