HP1 molecule C-terminal domain. Computer model showing the structure of the C terminal (shadow chromo) domain of a heterochromatin protein 1 (HP1) molecule from a mouse. Heterochromatin is a tightly packaged form of DNA (deoxyribonucleic acid). HP1 proteins are highly conserved adapter proteins that have important functions in the cell nucleus. They are fundamental units of heterochromatin packaging that are found at the centromeres and telomeres of nearly all eukaryotic chromosomes. Members of the HP1 family are characterised by an N-terminal chromo domain and a C-terminal shadow chromo domain (shown here), separated by a Hinge region.