Figure 3.

Energy profiles and DNA twisting for the chromatin fibers with the linkers L = 20 (A, C, and E) and 25 bp (B, D, and F). Each point corresponds to a minimum of the conformation energy in the space of three fiber parameters—radius, rise, and polar angle φ (Fig. 1A). Energy is very high for ρ < –120° so this region is omitted for clarity. (A and B) Total energy. (C and D) Torsional energy of the linker DNA. (E and F) Changes in the excess twisting, ΔTw, of the linker DNA as a function of the inclination angle ρ. The points shown by asterisks in (C)–(F) correspond to the linker DNA undertwisted or overtwisted by more than 180°. (See the main text for details.)