Multiple dense phases of nucleosome core particles (NCPs) were formed in controlled ionic conditions (15-160 mM monovalent salt, no divalent ions), under osmotic pressures ranging from 4.7 × 105 to 2.35 × 106 Pa. We present here the x-ray diffraction analysis of these phases. In the lamello-columnar phase obtained at low salt concentration (<25 mM), NCPs stack into columns that align to form bilayers, kept separated from one another by a layer of solvent. NCPs form a monoclinic lattice in the plane of the bilayer. For high salt concentration (>50 mM), NCPs order into either a two-dimensional columnar hexagonal phase or into three-dimensional orthorhombic (quasi-hexagonal) crystals. The lamellar and hexagonal (or quasihexagonal) organizations coexist in the intermediate salt range; their demixing requires a long time. For an applied pressure P= 4.7 105 Pa, the calculated NCPs concentration ranges from ∼280 to 320 mg/ml in the lamello-columnar phase to 495 to 585 mg/ml in the three-dimensional orthorhombic phase. These concentrations cover the concentration of the living cell.
Mangenot, S., Leforestier, A., Durand, D., & Livolant, F. (2003). X-ray diffraction characterization of the dense phases formed by nucleosome core particles. Biophysical Journal, 84(4), 2570–2584. https://doi.org/10.1016/S0006-3495(03)75062-0