Figure 5.

(a) Basepair centers of an ideal, smoothly deformed, left-handed superhelical scaffold of 43.3 Å radius and 32.2 Å pitch (lightly shaded tube) superimposed on the central 80 bp of the DNA in the currently best-resolved nucleosome core-particle structure (gray block/ribbon representation of the observed pathway of bases/phosphates) (2). The idealized DNA bends smoothly via sinusoidal-like variation in Tilt and Roll and deforms out of the plane through the uniform decrease of Twist, differing from the periodic changes in Roll and Slide that contribute to the curvature and pitch of nucleosomal DNA (40). (b) Root mean-square deviation of the base and backbone atoms at each of the central 80 basepair steps of the smooth superhelical model compared to the crystallographically observed positions (2).