Fig. 4.

Comparison between the observed behavior and the calculations on a two-angle model of the nucleosome fiber. In the central plot, the Kuhn length $K_{\mathrm{n}m}$ is reported as a function of the compaction $c_{10}$ in nucleosomes per 10 nm. Active domains are represented by the observed power law (red thick line), while for inactive and repressed domains, we directly reported the measured values from Table 1 (black and blue dots, respectively). The colored dot-line plots correspond to the same physical quantities calculated on the basis of the two-angle model in a large range of wrapping angles, going from a completely wrapped nucleosome (angle $\sim {50}^{\circ }$) to a largely open one (angle $\sim -{30}^{\circ }$). The angle dependence is explicitly accounted for in the four lateral plots. Two cases with NRL = 182 bp (blue-green) and NRL $=$ 152 bp (purple-orange) are reported here. The four displayed fibers are completely regular fibers obtained by using the two-angle model for the following parameter sets : $\text{angle}={50}^{\circ }$, NRL $=$ 152 bp (yellow-orange fiber); $\text{angle}=-{22}^{\circ }$, NRL $=$ 152 bp (purple fiber); $\text{angle}={50}^{\circ }$, NRL = 182 bp (yellow-green fiber); $angle=-{22}^{\circ }$, NRL $=$ 182 bp (blue-green fiber). For each fiber picture, the length corresponds precisely to one Kuhn length as calculated from the corresponding parameter set