Fig. (5) Binding pockets of four representative PHD fingers: A) PHF21A (BHC80) bound to unmethylated H3K4 (PDB: 2PUY). B) PHF13 bound to H3K4me3 (PDB: 3O7A). C) PYGO1 bound to H3K4me2 (PDB: 2VPE). D) BPTF bound to H3K4me3 (PDB: 2F6J). In all four structures, PHD domains are shown in yellow ribbon and histone tails are shown in red ribbon. Protonated methyl-lysines (unmethylated H3K4 in 5A) and trimethyl-lysines are displayed in ball and stick model with gray carbon atoms. Key binding site residues of the PHD fingers are displayed in stick model with white carbon atoms.