Structure of the Nucleosome
The nucleosome is the basic repeating unit of chromatin structure. Double stranded DNA wraps around a nucleosome core containing eight histone proteins: an H3-H4 tetramer and two H2A-H2B dimers. The histone amino acid sequences have been one of the most highly conserved during all of eukaryotic evolution.
The 147 bp of DNA in this structure is shown as Sticks, colored red and yellow. The proteins are shown as Cartoons. Histone H3 is colored blue; H4 is green; H2A is cyan; and H2B is magenta. The histones are mostly a-helical and all four have a similar architecture, the so-called "histone fold".
- Highlights
Histones & DNA: This button restores the original display and coloring of the model.
- Histones or DNA: Successive clicks on this "toggle" button switches between the DNA and protein components of the model.
- "Top" or "Bottom" Half: Successive clicks display the two symmetrically related halves of the structure. The four histones are labeled at their N-termini.
- Side View: The Spacefilled protein is colored light green.
- Lys + Arg Residues: The positively-charged side chains of these amino acids are colored blue. Histones help to neutralize the negative charges on the DNA phosphate groups. There is very little DNA-sequence specificity in nucleosome assembly, i.e. just what one would expect for the principal DNA packaging protein of the nucleus.
- Acetylated Lys Residues: Twenty Lys residues are known to be acetylated by various histone acetyl transferases (HATs). Acetylation of the e-amino group neutralizes the positive charge on the lysines. As a result, the chromatin becomes more "open" to the binding of transcriptional (and other) factors.
Each of the buttons leaves the highlighted features "selected" to permit a choice of additional display or coloring from the Chime menu.
The structure of the nucleosome is described by:
Davey CA, Sargent DF, Luger K, Maeder AW, Richmond TJ. (2002) "Solvent mediated interactions in the structure of the nucleosome core particle at 1.9 Å resolution." J Mol Biol 319: 1097 PubMed [1KX5.pdb]
|
Back to the Protein Structure List.
Return to Home Page Fall 2004 -or- Home Page Spring 2004.