Figure 1. In the textbook model, a long DNA molecule is wrapped around a basic core histone octamer that consists of H2A, H2B, H3 and H4 histone proteins, and forms a nucleosome with a diameter of 11 nm. The nucleosome has long been assumed to be folded into 30-nm chromatin fibers before the higher-order organization of mitotic chromosomes or interphase nuclei occurs. We show a typical one-start helix model between two well-known structural models for 30-nm chromatin fibers: one-start helix (solenoid) and two-start helix (zigzag). The images are reproduced with minor modifications fromreference 60 with permission from Elsevier.