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(A and B) Electron microscopic evidence for the top and bottom-left model structures depicted in (C). (C) Zigzag variations. An interconversion between these three variations is proposed to occur by an accordion-like expansion and contraction of the fiber length. Differences in the length of the linker between adjacent nucleosome beads can be accommodated by snaking or coiling of the linker DNA, or by small local changes in the width of the fiber. Formation of the 30-nm fiber requires both histone H1 and the core histone tails; for simplicity, neither is shown here, but see Figures 4-30 and 4-32. (From J. Bednar et al., Proc. Natl. Acad. Sci. USA 95:14173 14178, 1998. © National Academy of Sciences.)
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