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EMBO J. 2016 May 17;35(10):1115-32. doi: 10.15252/embj.201592660. Epub 2016 Apr 12.

Nucleosomal arrays self-assemble into supramolecular globular structures lacking 30-nm fibers.

Author information

1
Biological Macromolecules Laboratory, Structural Biology Center, National Institute of Genetics and Department of Genetics, Sokendai (Graduate University for Advanced Studies), Mishima, Japan RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Japan kmaeshim@nig.ac.jp jeffrey.c.hansen@colostate.edu.
2
Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO, USA.
3
Biological Macromolecules Laboratory, Structural Biology Center, National Institute of Genetics and Department of Genetics, Sokendai (Graduate University for Advanced Studies), Mishima, Japan.
4
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Japan XFEL Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI), Sayo-gun, Japan.
5
RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Japan.
6
Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO, USA kmaeshim@nig.ac.jp jeffrey.c.hansen@colostate.edu.

Abstract

The existence of a 30-nm fiber as a basic folding unit for DNA packaging has remained a topic of active discussion. Here, we characterize the supramolecular structures formed by reversible Mg(2+)-dependent self-association of linear 12-mer nucleosomal arrays using microscopy and physicochemical approaches. These reconstituted chromatin structures, which we call "oligomers", are globular throughout all stages of cooperative assembly and range in size from ~50 nm to a maximum diameter of ~1,000 nm. The nucleosomal arrays were packaged within the oligomers as interdigitated 10-nm fibers, rather than folded 30-nm structures. Linker DNA was freely accessible to micrococcal nuclease, although the oligomers remained partially intact after linker DNA digestion. The organization of chromosomal fibers in human nuclei in situ was stabilized by 1 mM MgCl2, but became disrupted in the absence of MgCl2, conditions that also dissociated the oligomers in vitro These results indicate that a 10-nm array of nucleosomes has the intrinsic ability to self-assemble into large chromatin globules stabilized by nucleosome-nucleosome interactions, and suggest that the oligomers are a good in vitro model for investigating the structure and organization of interphase chromosomes.

KEYWORDS:

10‐nm chromatin fiber; X‐ray scattering; analytical ultracentrifugation; microscopy; nucleosomal array

PMID:
27072995
PMCID:
PMC4868957
DOI:
10.15252/embj.201592660
[Indexed for MEDLINE]
Free PMC Article

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