Figure 2.

Two-start chromatin fibers with the linker L = 20 bp, with the inclination angle ρ changing from ±180° to 150°. All conformations correspond to the energetically optimal points (Fig. 3A). Note that all these structures are different—in particular, the fiber with ρ = –90° differs from the fiber with ρ = 90° (see positions of the DNA entry points shown as red balls). The DNA is presented in alternating blue and orange colors, to emphasize the two stacks of nucleosomes and to clarify the passage of linkers in the middle of the fiber. The histone cores are also shown in two colors: the entry sides of nucleosomes (interacting with the DNA entry points shown as red balls) are colored in yellow, and the exit sides are in white. In this way, it is easier to distinguish the fiber configurations. For example, for ρ = 0 the white sides of the cores face upward, whereas for ρ = 180° they face downward. To see this figure in color, go online.