Journal
NUCLEUS
Volume 3, Issue 5, Pages 404-410Publisher
TAYLOR & FRANCIS INC
DOI: 10.4161/nucl.21222
Keywords
30-nm chromatin fiber; chromatin; cryo-EM; fractal nature; interphase nuclei; irregular folding; mitotic chromosomes; X-ray scattering
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Funding
- MEXT
- JST CREST
- Grants-in-Aid for Scientific Research [22657044, 23651126, 22540424, 22310075, 23370078] Funding Source: KAKEN
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How is a long strand of genomic DNA packaged into a mitotic chromosome or nucleus? The nucleosome fiber (beads-on-a-string), in which DNA is wrapped around core histones, has long been assumed to be folded into a 30-nm chromatin fiber, and a further helically folded larger fiber. However, when frozen hydrated human mitotic cells were observed using cryoelectron microscopy, no higher-order structures that included 30-nm chromatin fibers were found. To investigate the bulk structure of mitotic chromosomes further, we performed small-angle X-ray scattering (SAXS), which can detect periodic structures in noncrystalline materials in solution. The results were striking: no structural feature larger than 11 nm was detected, even at a chromosome-diameter scale (similar to 1 mu m). We also found a similar scattering pattern in interphase nuclei of HeLa cells in the range up to similar to 275 nm. Our findings suggest a common structural feature in interphase and mitotic chromatins: compact and irregular folding of nucleosome fibers occurs without a 30-nm chromatin structure.
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