Chromatin Structure: Nucleosome Formation and Positioning

TL;DRAbstract

In all eukaryotic cells the DNA is complexed with a group of highly basic histone proteins forming nucleosomes and higher order chromatin structures. In the nucleosome the DNA is tightly wrapped, almost two turns, around an octamer of histone proteins. The octamer in turn is built as a tripartite assembly of a (H3/H4)2-tetramer flanked by two (H2A/H2B)-dimers. The tripartite nature exhibits an interesting feature upon nucleosome formation. The nucleosomal wrapping about the tetramer complex is stabilised energetically four-fold by the addition of the dimers. In addition, the histone octamer is designed to bind virtually all sequences that exist in the genome, but intrinsic properties of the DNA, such as curvature and flexibility, modulate the association of a particular stretch with the histone octamer. The protruding histone terminal tails also contribute to nucleosome stability. The tails help folding on the mononucleosomal level of intrinsically static DNA, but not for flexible DNA.

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