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

Abstract

SynopsisThe 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 f 0.1 turns of DNA are wrapped a t 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.

Structural studies of proteins by high-flux X-ray and neutron solution scattering

“…A full contrast variation study based on I(Q) measured in several contrasts has led to the three basic scattering functions Iv(Q), IVF(Q) and IF(Q) (Hjelm et al, 1977;Suau et al, 1977). These summarize all the data on the external I, and internal IF structures, together with their cross-term IVF-These permitted the development of Debye sphere models to define the basic structural model for the nucleosome in terms of a DNA superhelix wound 1.75 times around an octamer of eight core histone proteins (Braddock et al, 1981). Further experiments have studied other solution properties of this protein-DNA complex.…”

On the biological role of histone acetylation

“…With the technique of neutron scatter it is possible to determine with high accuracy the shape of nucleosome core particles in solution (Hjelm et al, 1977;Suau et al, 1977;Pardon et al, 1977;Braddock et al, 1981). With this technique no sign of unfolding could be detected in hyperacetylated nucleosome core particles with 2.4 acetates per H4 molecule (Imai et al, 1986).…”

Neutron scattering studies and modeling of high mobility group 14 core nucleosome complex.

“…Although the general structure of the nucleosome core particle is fairly well established (3)(4)(5)(6), little is known about the dynamics ofthe structure and the interaction ofpotential effector proteins such as ubiquitin or the high mobility group (HMG) nonhistone chromosomal proteins. HMG 14 and HMG 17 are categorized as structural proteins that are associated wth potentially active regions of chromatin (7).…”