Different conformations adopted by the H4 C-terminal tail within the nucleosome and when bound to anti-silencing function 1 (Asf1). (A) Ribbon diagram showing the overall structure of the Asf1-H3/H4 complex (PDB:2HUE) , with Asf1 (violet), H3 (blue), and H4 (green). G94 is shown in red and the H4 C-terminal tail is circled in red. (B) Ribbon diagram showing the histone H3/H4 heterotetramer from the nucleosome core particle (PDB:1KX5)  oriented so that the H3/H4 dimer on the left is superimposed with the H3/H4 dimer in (A). Structures are colored as in (A) with H2A in yellow. (C) The amino acid sequence of the H4 C-terminal tail is shown with G94 in red aligned with the α3 helix and C-terminal β strand (βC) illustrated for H4 in the Asf1-H3/H4 complex and the nucleosome core particle (NCP), respectively.