Research Article

Cryo-EM Study of the Chromatin Fiber Reveals a Double Helix Twisted by Tetranucleosomal Units

Science  25 Apr 2014:
Vol. 344, Issue 6182, pp. 376-380
DOI: 10.1126/science.1251413

You are currently viewing the abstract.

View Full Text

Via your Institution

Log in through your institution

Log in through your institution


Double Helix, Doubled

Chromatin consists of genomic DNA packaged onto nucleosomes—double donut-shaped complexes of histone proteins. Roughly 150 base pairs of DNA are wrapped around each nucleosome with variable lengths of linker DNA in-between. Using cryogenic electron microscopy, Song et al. (p. 376; see the Perspective by Travers) determined the 11 angstrom–resolution structure of a 12-nucleosome string of DNA. The segment forms a 30-nanometer fiber structure, which is itself double-helical, like the DNA it packages.

Abstract

The hierarchical packaging of eukaryotic chromatin plays a central role in transcriptional regulation and other DNA-related biological processes. Here, we report the 11-angstrom–resolution cryogenic electron microscopy (cryo-EM) structures of 30-nanometer chromatin fibers reconstituted in the presence of linker histone H1 and with different nucleosome repeat lengths. The structures show a histone H1-dependent left-handed twist of the repeating tetranucleosomal structural units, within which the four nucleosomes zigzag back and forth with a straight linker DNA. The asymmetric binding and the location of histone H1 in chromatin play a role in the formation of the 30-nanometer fiber. Our results provide mechanistic insights into how nucleosomes compact into higher-order chromatin fibers.

View Full Text