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 \(K_{\mathrm nm}\) 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 : \(\hbox {angle} = 50^\circ\), NRL \(=\) 152 bp (yellow-orange fiber); \(\hbox {angle} = -22^\circ\), NRL \(=\) 152 bp (purple fiber); \(\hbox {angle} = 50^\circ\), 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