Stereo image showing the 1.90 Å octamer (PDB code http://www.rcsb.org/pdb/cgi/explore.cgi?pdbId=1tzy). The colour coding is H2A, cyan; H2B, light green; H3, red; H4, yellow; H2A′, magenta; H2B′, grey; H3′, blue; H4′, brown. The H2A–H4′ and H2A′–H4 docking regions are shown in black.