Chromatin fiber dimensions and nucleosome orientation : a neutron scattering investigation

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Abstract
Chromatin fibers were studied in solutions of mM monovalent salt by small angle neutron scattering. The variation of the cross section radius of gyration with H2O/D2O contrast shows that DNA is at much larger average radial distances from the fiber axis than histone. Consequently, the coils of DNA in a core particle must be approximately parallel to the fiber direction. The radii of gyration suggest that the maximum diameter of chromatin and nucleosomes is ∼ 14 nm and that the DNA is distributed in two radial layers. The concentration dependence of the scattering maxima near 14 nm spacings furnishes independent support for a 14 nm external diameter and can be interpreted by a double DNA layer configuration.