The superstructure of chromatin and its condensation mechanism. II. Theoretical analysis of the X-ray scattering patterns and model calculations.

Model calculations on the superstructure of uncondensed and condensed chromatin are presented. It is found that agreement between the calculated X-ray solution scattering patterns and the experimental observations can be reached with the assumptions that: a) The uncondensed chromatin fibre in solution has a helix-like structure, with a pitch of ca. 33.0 nm, a helical diameter of ca. 20.0 nm and 2.75-3.25 nucleosomes per turn. b) The most condensed state of the chromatin fibre in solution is best represented by a helix-like structure with ca. 2.56 nucleosomes per turn, a pitch of ca. 3.0 nm and a helical diameter of ca. 27.0 nm.