FIGURE 8-26 Post-translational modifications observed on human histones. (a) Model of a nucleosome viewed from the top with histones shown as ribbon diagrams. This model depicts the lengths of the histone tails (dotted lines), which are not visible in the crystal structure (see Figure 8-24). The H2A N-terminal tails are at the bottom, and the H2A C-terminal tails are at the top. The H2B N-terminal tails are on the right and left, and the H2B C-terminal tails are at the bottom center. Histones H3 and H4 have short C-terminal tails that are not modified. (b) Summary of post-translational modifications observed in human histones. Histone-tail sequences are shown in the one-letter amino acid code (see Figure 2-14). The main portion of each histone is depicted as an oval. These modifications do not all occur simultaneously on a single histone molecule. Rather, specific combinations of a few of these modifications are observed on any one histone. See K. Luger and T. J. Richmond, 1998, Curr. Opin. Genet. Devel. 8:140.

[Part (a) data from K. Luger et al., 1997, Nature 389:251, PDB ID 1aoi. Part (b) data from R. Margueron et al., 2005, Curr. Opin. Genet. Devel. 15:163.]