Structural model of the nucleosome. (a) The simplified structure of a nucleosome octamer (left), with DNA wrapped around the histone core (right). (b) A ribbon representation of the structure of the nucleosome from the African frog Xenopus laevis, with different colors representing the five histones, matching the colors in (a). The view in (b) is rotated relative to the view in (a) to show one face of the nucleosome. (c) Surface representation of the nucleosome. A 146 bp segment of DNA binds in a left-handed solenoidal supercoil that circumnavigates the histone complex 1.67 times. The orientation in (c) is the same as that in (a) to show the DNA wrapping around the nucleosome.