Crystal structures of human nucleosomes containing histone H2A.Z.1 or H2A.Z.2. (a) Alignment of the human H2A, H2A.Z.1 and H2A.Z.2 amino-acid sequences. The secondary structure of H2A.Z in the nucleosome is shown at the top of the panel. Amino-acid residues that differ among H2A.Z.1, H2A.Z.2 and H2A are represented with a white background. (b) Purified nucleosomes containing either H2A.Z.1 or H2A.Z.2 were analyzed by 6% nondenaturing PAGE. DNA was visualized by EtBr staining. (c) The histone composition of the purified nucleosomes was analyzed by 18% SDS–PAGE. Histones were visualized by Coomassie Brilliant Blue staining. (d) Crystal structure of the nucleosome containing human histone H2A.Z.1. Two views are presented and the H2A.Z.1 molecules are coloured blue. The L1 loop region of H2A.Z.1 is enlarged and presented at the top of the right panel. (e) Crystal structure of the nucleosome containing human histone H2A.Z.2. Two views are presented and the H2A.Z.2 molecules are coloured magenta. The L1 loop region of H2A.Z.2 is enlarged and presented at the top of the right panel.