Heterochromatin protein that acts as a transcription repressor and has the ability to promote the formation of large heterochromatic domains. May act by recruiting heterochromatin proteins such as CBX5 (HP1 alpha), HDAC5 and MBD1. Represses IGF2 expression by binding to its CpG-rich P3 promoter and recruiting heterochromatin proteins. At specific stages of Listeria infection, in complex with TRIM28, corepresses interferon-stimulated genes, including IFNL1, IFNL2 and IFNL3. Interacts with CBX5 (HP1 alpha), HDAC5, MBD1 and SP1. Forms a transcription silencing complex with at least CBX3 (HP1 gamma), HDAC1, HDAC2 and TRIM28. Interacts with L.monocytogenes LntA; this interaction, occurring at a late Listeria infection stage, relieves transcription repression, mostly that of interferon-stimulated genes. Localizes to heterochromatin and inactive X chromosome. Colocalizes with histone H3 trimethylated at 'Lys-27' (H3K27me3). The BAH domain is required for localization at H3K27me3. Extended N-terminus.