Figure 3.

Typical conformations of chromatin fiber with NRL = 167 bp simulated for external forces increasing from 0 to 8 pN. Our comparative analysis reveals that at small forces, F ≤ 3.0 pN, the DNA unwrapping is insignificant, U ≤ 12 bp, and the fiber remains relatively compact despite numerous stacking-unstacking events. With an increase in applied force, the unwrapping of nucleosomal DNA becomes more pronounced and increases to U = 20 bp at F = 4 pN and up to U = 32 bp at F = 8 pN. These MC simulations were performed for stacking energy E = 8 kT. Note, however, that for F = 3.5 pN and higher, the internucleosome stacking is lost completely, and therefore, the results do not depend on the E value. The force-unwrapping, force-extension, and force-unstacking dependencies are presented at the bottom. Fiber conformations for NRL = 197 bp are presented in Fig. S6 (see also the Video S1 and S2). To see this figure in color, go online.