Neutron scattering of chromatin multinucleosomes

Abstract Neutron scattering data for multinucleosomes are analysed to give distance-distribution functions D ( u ), of the cross section of high multimers (≫50 mers). Although the diameter of the folded structure is closely similar for multinucleosomes from inactive chromatin in chick erythrocytes compared with more active chromatin in calf thymus, the shape of the D ( u ) curves are different: the calf-thymus multinucleosomes have a much higher most-probable distance in the cross-section. Analysis of data to give D ( u ) functions from three-dimensional structures containing ∼23 nucleosomes from chick erythrocytes, fixed and unfixed, shows that the multinucleosome particles are not spherical and fit a rod-like model with the centre of the rod filled with scattering material. This extends the analysis published earlier [10, 12]. Folding of chromatin by Mg ++ ions depends on the concentration of these ions per DNA phosphate and hence depends on the chromatin concentration.