page_title: Nucleosome
section_title: Structure of the core particle
hierarchical_section_title: Nucleosome / Structure / Structure of the core particle
caption_attribution_description: PDB: 1KX5&#8203;
context_page_description: A nucleosome is the basic structural unit of DNA packaging in eukaryotes. The structure of a nucleosome consists of a segment of DNA wound around eight histone proteins and resembles thread wrapped around a spool. The nucleosome is the fundamental subunit of chromatin. Each nucleosome is composed of a little less than two turns of DNA wrapped around a set of eight proteins called histones, which are known as a histone octamer. Each histone octamer is composed of two copies each of the histone proteins H2A, H2B, H3, and H4.
  DNA must be compacted into nucleosomes to fit within the cell nucleus. In addition to nucleosome wrapping, eukaryotic chromatin is further compacted by being folded into a series of more complex structures, eventually forming a chromosome.
  Nucleosomes are thought to carry epigenetically inherited information in the form of covalent modifications of their core histones. Nucleosome positions in the genome are not random, and it is important to know where each nucleosome is located because this determines the accessibility of the DNA to regulatory proteins.
caption: The crystal structure of the nucleosome core particle consisting of  H2A ,  H2B ,  H3  and  H4  core histones, and DNA. The view is from the top through the superhelical axis.
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