The structure of chromatin
(a) The nucleosome in decondensed and condensed chromatin. (b) End view of the coiled chain of nucleosomes. (c) Chromatin structure varies along the length of a chromosome. The least-condensed chromatin (euchromatin) is shown in yellow, regions of intermediate condensation are in orange and blue, and heterochromatin coated with special proteins (purple) is in red.
[(c) From P. J. Horn and C. L. Peterson, “Chromatin Higher Order Folding: Wrapping Up Transcription,” Science 297, 2002, 1827, Fig. 3. Copyright 2002, AAAS]