Figure 1.

(A) Schematic description of the six-angle model of chromatin. The nucleosomes are connected by pieces of elastic DNA with length l (depicted as springs). The nucleosomes are shown as cylinders; however, they are represented by an anisotropic potential as spherocylindrical particles. The angles α, γ, and β describe the DNA path between consecutive nucleosomes, and ϕ, ɛ, and δ describe the nucleosome orientation relative to the incoming and outgoing linker DNA. The parameter c is the distance from the center of the histone core to the start of the linker DNA and can describe a nucleosome stem structure (16,17). The gap between the two DNA strands leaving and entering the chromatosome core particle at this point is denoted by d. For more details, see the Supporting Material. (B) Denotation of the chromatin fiber structures by nucleosome stacks and DNA path according to Depken and Schiessel (37). A sample fiber structure is shown (left: side view, right: top view). A helical winding of the chain is described by [N_stack, N_step], where N_stack is the number of nucleosome stacks and N_step is the step size across stacks between connected nucleosomes. A seven-start helix with different linker DNA paths (black lines) is shown with solenoidal ([7, 1]) and crossed-linker DNA ([7, 2] and [7, 3]) paths. The dashed line marks the linker DNA to the nucleosome of the next turn.