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| Title | Evidence for short-range helical order in the 30-nm chromatin fibers of erythrocyte nuclei. |
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| Journal, issue, pages | Proc Natl Acad Sci U S A, Vol. 108, Issue 41, Page 16992-16997, Year 2011 |
| Publish date | Oct 11, 2011 |
 Authors | Margot P Scheffer / Mikhail Eltsov / Achilleas S Frangakis /  |
| PubMed Abstract | Chromatin folding in eukaryotes fits the genome into the limited volume of the cell nucleus. Formation of higher-order chromatin structures attenuates DNA accessibility, thus contributing to the ...Chromatin folding in eukaryotes fits the genome into the limited volume of the cell nucleus. Formation of higher-order chromatin structures attenuates DNA accessibility, thus contributing to the control of essential genome functions such as transcription, DNA replication, and repair. The 30-nm fiber is thought to be the first hierarchical level of chromatin folding, but the nucleosome arrangement in the compact 30-nm fiber was previously unknown. We used cryoelectron tomography of vitreous sections to determine the structure of the compact, native 30-nm fiber of avian erythrocyte nuclei. The predominant geometry of the 30-nm fiber revealed by subtomogram averaging is a left-handed two-start helix with approximately 6.5 nucleosomes per 11 nm, in which the nucleosomes are juxtaposed face-to-face but are shifted off their superhelical axes with an axial translation of approximately 3.4 nm and an azimuthal rotation of approximately 54°. The nucleosomes produce a checkerboard pattern when observed in the direction perpendicular to the fiber axis but are not interdigitated. The nucleosome packing within the fibers shows larger center-to-center internucleosomal distances than previously anticipated, thus excluding the possibility of core-to-core interactions, explaining how transcription and regulation factors can access nucleosomes. |
 External links | Proc Natl Acad Sci U S A / PubMed:21969536 / PubMed Central |
| Methods | EM (subtomogram averaging) |
| Resolution | 43.1 Å |
| Structure data |  EMDB-1781:  EMDB-1782: |
| Source |
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Gallus gallus (chicken)