Figure 4.

Response under topological deformation of a chromatosome fiber after treatment with heparin. We show a comparison of extension-versus-rotation of a chromatosome fiber (left) and its corresponding nucleosome fiber (right). Linker histones were removed specifically by injecting heparin at a concentration of 1 μg/mL in buffer B0. Both exhibit the typical hysteretic behavior of chromatin fibers. (Middle panel) Comparison between forward curves of the chromatosome fiber (pink) and the nucleosome fiber (purple). One can observe a lengthening (δL) due to removal of linker histones which is ∼200 nm. A slight shift in topology (δR), i.e., in the linking number, is also observable toward positive values after linker histone removal. It is estimated to be ∼0.5 per particle. (Red) Response of the corresponding naked DNA (the asymmetry of its response is due to the denaturation of DNA occurring under negative supercoiling (17)).