The layered organization of nucleosomes in 30 nm chromatin fibers

Abstract

We have used electron microscopy and established methods of three-dimensional reconstruction to obtain structural information on the 30 nm chromatin fibers from sea cucumber sperm and chicken erythrocytes. The fibers show a longitudinal periodicity of 10-11 nm. We have interpreted this periodicity as due to a grouping of nucleosomes into disks, each disk containing about 5-6 nucleosomes. These disks are closely stacked to form the chromatin fiber. We have built a detailed model for four fibers and we have determined the approximate coordinates of all the nucleosomes in them. The average distance found between neighboring nucleosomes has a value close to 11 nm. They may be connected either as a regularly distorted helix or as a layered zigzag. The second model appears more appropriate, since in the constrictions of the fibers the nucleosomes can only be connected as a zigzag.

The Detailed 3D Multi-Loop Aggregate/Rosette Chromatin Architecture and Functional Dynamic Organization of the Human and Mouse Genomes

“…This is also consistent with a variety of compacted structures described throughout the literature (see e.g. [29,30,32,33]), the absolute nucleosome concentration distributions [35,36], the dynamic and functional properties such as the architectural stability and movement of chromosomes [3,5,39,62,64], chromatin dynamics [38], as well as the diffusion of molecules inside nuclei (e.g. [5,39,64] Figure S1).…”

“…In contrast other and especially more recent suggestions range from basically no compaction at all (rev. [26][27][28]), to highly polymorphic compacted [29,30] nucleosome position [31] and function-dependent structures [32,33]. The latter are essential to explain nucleosome concentration distributions [34][35][36][37], or chromatin dynamics [38] and functional properties such as the nuclear diffusion of macromolecules [5,39].…”

Tomographic three-dimensional reconstruction of cilia ultrastructure from thick sections.

“…11). Only a few studies report the reconstruction of larger cellular components such as chromatin (12,13) and Balbiani rings (14,15). Chromosomes, however, are not the ideal object with which to assess the value of applying tomographic methods to thick-section reconstructions because their structure lacks clearly defined features, is not well established, and varies with the isolation procedure.…”

Electrophoresis of Chromatin on Nondenaturing Agarose Gels Containing Mg2+

“…The mechanism of chromatin folding and the structure of the 30-nm fiber have been studied by sedimentation methods (7)(8)(9), enzymatic and chemical digestions (10 -12), electric, flow, and photochemical dichroism (13)(14)(15)), x-ray diffraction (16,17), small angle x-ray scattering (18 -20), neutron scattering (21,22), transmission electron microscopy (23)(24)(25)(26)(27)(28)(29)(30)(31)(32), and scanning force microscopy (33). The results obtained in these studies have suggested different models for the folding and structural organization of the 30-nm chromatin fiber.…”

“…In the twistedribbon models, a two-start helix is formed by pairs of nucleosomes with the linker DNA parallel to the fiber axis (24,26). Finally, in several continuous (11,18,28) and discontinuous (27) crossed-linker models, and in the variable zigzag nucleosomal ribbon model (30,31), the linker DNA is extended in the fiber interior.…”