Function: Transcriptional repressor that binds CpG islands in promoters where the DNA is methylated at position 5 of cytosine within CpG dinucleotides. Binding is abolished by the presence of 7-mG that is produced by DNA damage by methylmethanesulfonate (MMS). Acts as transcriptional repressor and plays a role in gene silencing by recruiting AFT7IP, which in turn recruits factors such as the histone methyltransferase SETDB1. Probably forms a complex with SETDB1 and ATF7IP that represses transcription and couples DNA methylation and histone 'Lys-9' trimethylation. Isoform 1 and isoform 2 can also repress transcription from unmethylated promoters. Tissue specificity: Widely expressed. Similarity: Contains 3 CXXC-type zinc fingers. Contains 1 MBD (methyl-CpG-binding) domain. Domain: The methyl-CpG-binding domain (MBD) functions both in binding to methylated DNA and in protein interactions. The third CXXC-type zinc finger mediates binding to non-methylated CpG dinucleotides. The transcriptional repression domain (TRD) is involved in transcription repression and in protein interactions. PTM: Sumoylated with SUMO1 by PIAS1 and PIAS3. Sumoylation affects transcriptional silencing by preventing the interaction with SETDB1. In contrast, sumoylation may increase interaction with AFT7IP. Phosphorylated upon DNA damage, probably by ATM or ATR.