title: Physical studies of chromatin. The recombination of histones with DNA.
abstract: Experiments have been carried out to define clearly which histone combinations can induce a higher order structure when combined with DNA. The criterion for a higher order structure being the series of low-angle X-ray diffraction maxima nominally at 5.5 nm, 3.7 nm, 2.7 nm and 2.2 nm. Such a pattern, with resolution similar to that of H1-depleted chromatin, is readily attainable by recombining histones H2A + H2B + H3 + H4 with DNA using a salt-gradient dialysis method. However, the use of urea in the recombination procedure is shown to be detrimental to the production of a higher order structure. Low-angle ring patterns are not obtained by recomgining DNA with single pure histones or any combination of histone pairs exept H3 + H4. The diffraction maxima from the latter are, however, weaker than those from chromatin and there are pronounced semi-equatorial arcs. The presence of a third histone, either H2A or H2B in the H3 + H4 recombination mixture tends to distort the recognised low-angle pattern. It is concluded that the histone pair H3 + H4 is essential for the formation of a regular higher order structure in chromatin, although for a complete structural development the presence of H2A + H2B is also required.
mesh_terms: D001665:Binding Sites; D002843:Chromatin / Q000648:ultrastructure*; D004247:DNA; D003956:Dialysis; D006657:Histones; D046911:Macromolecular Substances; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D011487:Protein Conformation; D014961:X-Ray Diffraction
chemical_list: D002843:Chromatin; D006657:Histones; D046911:Macromolecular Substances; D004247:DNA