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Figure 2.
Fig. 2. Nomenclature and schematic representation of
assemblies observed for several histones. The histone fold is
stylized here as a pointed N terminus representing the short
helix 1, a long central region representing the longer helix 2,
and a rounded C terminus representing the short helix 3. A
eukaryotic nucleosome is comprised of 145-147 bp of DNA and two
copies each of four histone proteins (H2A, H2B, H3, and H4)
(Thomas and Kornberg 1975; Arents and Moudrianakis 1995; Luger
et al. 1997). A complete nucleosome histone octomer may be
viewed as a left-handed spiral protein assembly constructed from
three subassemblies. (A) (Left) An HMk monomer contains two
histone-fold ms, the N- and C-terminal domains, tethered by a
13-residue loop. (Right) An HMk dimer formed through
crystallographic contacts associates through C-terminal helices
of the N-terminal domain. (B) (Left) The eight histone proteins
assemble as two copies each of two different heterodimers
(H2A-H2B and H3-H4) (Thomas and Kornberg 1975; Luger et al.
1997). (Center) [H3-H4] assembles as [H3-H4][2]. This complex
initiates DNA-binding, positions the nucleosome, and forms
stable nucleosomelike structures in complex with DNA (Dong and
van Holde 1991; Hayes et al. 1991). (Right) The nucleosome is
completed by adding [H2A-H2B] to each end of the [H3-H4][2]
tetramer.
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