Evidence for short-range helical order in the 30-nm chromatin fibers of erythrocyte nuclei.

摘要: Chromatin folding in eukaryotes fits the genome into limited volume of cell nucleus. Formation higher-order chromatin structures attenuates DNA accessibility, thus contributing to control essential functions such as transcription, replication, and repair. The 30-nm fiber is thought be first hierarchical level folding, but nucleosome arrangement compact was previously unknown. We used cryoelectron tomography vitreous sections determine structure compact, native avian erythrocyte nuclei. predominant geometry revealed by subtomogram averaging a left-handed two-start helix with approximately 6.5 nucleosomes per 11 nm, which are juxtaposed face-to-face shifted off their superhelical axes an axial translation 3.4 nm azimuthal rotation 54°. produce checkerboard pattern when observed direction perpendicular axis not interdigitated. packing within fibers shows larger center-to-center internucleosomal distances than anticipated, excluding possibility core-to-core interactions, explaining how transcription regulation factors can access nucleosomes.