title: Organisation of subunits in chromatin.
abstract: There is considerable current interest in the organisation of nucleosomes in chromatin. A strong X-ray and neutron semi-meridional diffraction peak at approximately 10 nm had previously been attributed to the interparticle specing of a linear array of nucleosomes. This diffraction peak could also result from a close packed helical array of nucleosomes. A direct test of these proposals is whether the 10 nm peak is truly meridional as would be expected for a linear array of nucleosomes or is slightly off the meridian as expected for a helical array. Neutron diffraction studies of H1-depleted chromatin support the latter alternative. The 10 nm peak has maxima which form a cross-pattern with semi-meridional angle of 8 to 9 degrees. This is consistent with a coil of nucleosomes of pitch 10 nm and outer diameter of approximately 30 nm. These dimensions correspond to about six nucleosomes per turn of the coli.
mesh_terms: D000818:Animals; D002417:Cattle; D002843:Chromatin / Q000648:ultrastructure*; D004247:DNA; D009502:Neutrons; D009690:Nucleic Acid Conformation; D013057:Spectrum Analysis; D013950:Thymus Gland / Q000648:ultrastructure; D014961:X-Ray Diffraction
chemical_list: D002843:Chromatin; D004247:DNA