Nucleosome features targeted by chromatin proteins. The nucleosome acidic patch created by histone H2A and H2B acidic residues (encircled) is frequently contacted by chromatin protein arginine residues. In addition, the histone H3 α1L1 elbow region of the histone fold (blue), the corresponding histone H2B α1L1 elbow (red) and the histone H2B C-terminal helix are sites of interaction by multiple chromatin proteins. The H2A, H2B, H3 and H4 core histones are shown in shades of yellow, red, blue and green respectively. The carbon side chain atoms of H2A acidic patch residues E61, D90 and E92 are shown in a more saturated yellow color.