HP1 alpha is a component of heterochromatin. It recognizes and binds histone H3 tails methylated at Lys-9, leading to epigenetic repression. HP1 alpha may interact with lamin B receptor (LBR). This interaction can contribute to the association of the heterochromatin with the inner nuclear membrane.
HP1 proteins are relatively small proteins (25 kDa) with a conserved amino-terminal chromo domain and a structurally related carboxy-terminal motif, the chromo shadow domain. Both domains of HP1 are required for binding to native chromatin in vivo, but they contribute differentially to binding in euchromatin and heterochromatin.