Comparison of the classic and chromovirus-derived chromodomains. Chromodomain structure of the heterochromatin protein 1 (HP1) family and diverse chromoviruses shown as alignment of multiple amino acid sequences. (A) Amino acid sequences of chromodomains of the HP1 proteins from Drosophila melanogaster (Dm-HP1) and Arabidopsis thaliana (At-LHP1), with the secondary structure illustrated at the top. The residues that constitute an aromatic cage are boxed in black and marked by asterisks. (B) In chromoviruses with group I chromodomains, the three conserved aromatic residues Y, W, and Y are present. (C) Group II chromodomain-containing chromoviruses usually lack the first and third conserved aromatic residue. (D) The CR motif of the centromeric Beetle chromoviruses is substantially diverged. Similar amino acids are shaded in grey.