title: Scatter analysis of discrete-sized chromatin fragments favours a cylindrical organization.
abstract: Fragments of chromatin containing 23 +/- 2.5 nucleosomes have been fractionated after light nuclease treatment of chicken erythrocyte nuclei. Low-angle scattering measures the total z-average radius of gyration of the already well-defined particles and the shape of scatter curves can be compared with three-dimensional analysis as opposed to cross-section analysis of long chromatin fragments. The data show that the particles are not spherical, have no detectable hole in the center of the structure and are best represented by a solid rod-like shape such as that generated by a coil of nucleosomes with the centre perhaps filled with linker DNA and histone H1/H5. 23 nucleosome fragments, where the DNA is partially fragmented, have near-identical scatter curves to the above-defined intact particles, indicating the primary importance of histone proteins in maintaining the integrity of the chromatin higher-order structure. Neutron scattering shows the radii of gyration to be contrast-independent, which fits in with the model calculations for solenoids. Particles with fragmented DNA and the intact particles, therefore, behave as sections of a solenoidal higher-order structure and possibly are observed as "superbeads' only during the folding and unfolding pathways of nucleosome multimers.
mesh_terms: D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D002645:Chickens; D002843:Chromatin / Q000097:blood / Q000648:ultrastructure*; D004912:Erythrocytes / Q000648:ultrastructure; D008433:Mathematics; D009502:Neutrons; D009707:Nucleosomes / Q000648:ultrastructure; D010316:Particle Size; D010446:Peptide Fragments / Q000097:blood*; D011487:Protein Conformation; D012542:Scattering, Radiation; D014965:X-Rays
chemical_list: D002843:Chromatin; D009707:Nucleosomes; D010446:Peptide Fragments