Original URL: http://info.bio.cmu.edu/Courses/03438/Nsome/1AOI.htm

Nucleosome Structure

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The Nucleosome Core Particle.
Eukaryotic chromatin is organized in a structural hierarchy. The smallest unit is the nucleosome, a complex between ~150 bp of DNA and two copies each of four histones. The DNA strands are colored green and brown. The histone coloring is: H3, blue; H4, light green; H2A, yellow; and H2B, red. Note the "histone-fold" in all four proteins. This is a structural motif comprised of three a-helices connected by two loops (a1-L1-a2-L2-a3). See the close-ups below for how they combine in the heterodimers to form crescent-shaped DNA-binding units.
(cf. Fig. 1a of Luger, et al.)
  Close-up view of the H3-H4 histone-fold pair.
  Highlight:Leu 65 (spacefill). Arg and Lys residues (blue).
    (cf. Fig. 2a of Luger, et al.)
  Close-up view of the H2A-H2B histone-fold pair.
  Highlight: Arg and Lys residues (blue).
    (cf. Fig. 2b of Luger, et al.)

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Coordinates from 1AOI.pdb. Luger, K. et al. (1997) "Crystal structure of the nucleosome core particle at 2.8 Å resolution". Nature 389 251.
The Header information from the 1AOI PDB file.