A hypothetical model of core PCAF/GCN5 complex interacting with nuleosome for histone acetylation. Shown in the bottom is a half nucleosome, which is made from the crystal structure solved by Luger et al . An oligomer of histone H3 and H4 is wrapped with two double-strand DNA helices. The N terminal tails of H3 and H4 are extended manually. The three subunits of the PCAF/GCN5 core complex, including Ada2 and Ada3, are drawn schematically as a heterohexamer. The arrows indicate experimentally verified interactions between histone tails, DNA double strands and all individual domains.