Neutron‐scattering studies of the structure of chromatin core particles in solution

The structure of the nucleosome core particle in solution has been studied by neutron scattering using the full‐contrast variation technique, which reduces the experimental spectra to three fundamental scatter functions holding information on shape and structure. Systematic calculations of the fundamental scatter functions expected from proposed core‐particle models have been compared with the observed functions and show that the neutron‐scattering criteria severely restrict the number of models which can be valid for the structure in solution. The best model for the core particle in solution has a hydrophobic histone core about which 1.7 ± 0.1 turns of DNA are wrapped at a pitch between 3.0 and 3.5 nm. This core contains most of the histone and has an average thickness of 4 nm and diameter 6.4–7.5 nm. While solution scattering is not able to specify uniquely the actual shape of the core to high resolution, all models which are possible for the shape of the core to a resolution justified by the data have been considered. It is clear that cylindrical or wedge shapes compatible with the above dimensions are valid structures. A hole probably penetrates the histone core, but the data do not allow a diameter greater than 1 nm. Available evidence suggests that about a quarter of the total histone is outside the core.