Component of heterochromatin that recognizes and binds histone H3 tails methylated at 'Lys-9' (H3K9me); leading to epigenetic repression. In contrast; it is excluded from chromatin when 'Tyr-41' of histone H3 is phosphorylated (H3Y41ph). Can interact with lamin-B receptor (LBR). This interaction can contribute to the association of the heterochromatin with the inner nuclear membrane. Involved in the formation of functional kinetochore through interaction with MIS12 complex proteins (By similarity). {ECO:0000250}.