Component of heterochromatin. Recognizes and binds histone H3 tails methylated at 'Lys-9', leading to epigenetic repression. Interaction with lamin B receptor (LBR) can contribute to the association of the heterochromatin with the inner nuclear membrane. Homodimer. Interacts directly with CHAF1A, EMSY, LBR, TIF1/TIF1A and TRIM28/TIF1B PXVXL motif via the chromoshadow domain. Interacts directly with histone H3 methylated at 'Lys-9' via the chromo domain. Interacts with SUV39H1 and SETDB1, SUV420H1 and SUV420H2. Interacts with PRDM6. Interacts with POGZ. Interacts with CHAMP1. Interacts with ASXL1. Expressed in all adult and embryonic tissues. Note: This description may include information from UniProtKB.