title: Nucleosomal arrays self-assemble into supramolecular globular structures lacking 30-nm fibers.
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.
authors.affiliation: 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.
authors.forename: Kazuhiro
authors.identifier: 0000-0003-3909-0341
authors.initials: K
authors.lastname: Maeshima
authors.affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO, USA.
authors.forename: Ryan
authors.initials: R
authors.lastname: Rogge
authors.affiliation: Biological Macromolecules Laboratory, Structural Biology Center, National Institute of Genetics and Department of Genetics, Sokendai (Graduate University for Advanced Studies), Mishima, Japan.
authors.forename: Sachiko
authors.initials: S
authors.lastname: Tamura
authors.affiliation: RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Japan XFEL Utilization Division, Japan Synchrotron Radiation Research Institute (JASRI), Sayo-gun, Japan.
authors.forename: Yasumasa
authors.initials: Y
authors.lastname: Joti
authors.affiliation: RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Japan.
authors.forename: Takaaki
authors.initials: T
authors.lastname: Hikima
authors.affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO, USA.
authors.forename: Heather
authors.initials: H
authors.lastname: Szerlong
authors.affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO, USA.
authors.forename: Christine
authors.initials: C
authors.lastname: Krause
authors.affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO, USA.
authors.forename: Jake
authors.initials: J
authors.lastname: Herman
authors.affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO, USA.
authors.forename: Erik
authors.initials: E
authors.lastname: Seidel
authors.affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: DeLuca
authors.affiliation: RIKEN SPring-8 Center, Sayo-cho, Sayo-gun, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Ishikawa
authors.affiliation: Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins, CO, USA kmaeshim@nig.ac.jp jeffrey.c.hansen@colostate.edu.
authors.forename: Jeffrey C
authors.identifier: 0000-0003-1857-4689
authors.initials: JC
authors.lastname: Hansen
mesh_terms: D004247:DNA / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D015636:Magnesium Chloride / Q000494:pharmacology; D008836:Micrococcal Nuclease / Q000378:metabolism; D009707:Nucleosomes / Q000187:drug effects / Q000378:metabolism*
chemical_list: D009707:Nucleosomes; D015636:Magnesium Chloride; D004247:DNA; D008836:Micrococcal Nuclease
keywords: 10‐nm chromatin fiber; X‐ray scattering; analytical ultracentrifugation; microscopy; nucleosomal array