X-ray diffraction characterization of the dense phases formed by nucleosome core particles

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Mangenot, Stéphanie | Leforestier, Amélie | Durand, Dominique | Livolant, Françoise

Edité par CCSD ; Biophysical Society -

International audience. 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.

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