Cryo-EM Study of the Chromatin Fiber Reveals a Double Helix Twisted by Tetranucleosomal Units
Feng Song1,2,*, Ping Chen1,*, Dapeng Sun1,2, Mingzhu Wang1, Liping Dong1,2, Dan Liang1,2, Rui-Ming Xu1, Ping Zhu1,†, Guohong Li1,†

1 National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China.
2 University of Chinese Academy of Sciences, Beijing 100049, China.

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.

Graphical Abstract

See more about this article:http://www.sciencemag.org/content/344/6182/376.long