The nucleosomal core histone octamer at 3.1 A resolution: a tripartite protein assembly and a left-handed superhelix.

Abstract

The structure of the octameric histone core of the nucleosome has been determined by x-ray crystaflography to a resolution of 3.1 A. The histone octamer is a tripartite assembly in which a centrally located (H3-H4)2 tetramer is flanked by two H2A-H2B dimers. It has a complex outer surface; depending on the perspective, the structure appears as a wedge or as a flat disk.The disk represents the planar projection of a left-handed proteinaceous superhelix with -28 A pitch. The diameter of the particle is 65 A and the length is 60 A at its maximum and -10 A at its Ium extension; these dimensions are in agreement with those reported earlier by Klug et al.

Visualization of Nucleosomal Substructure in Native Chromatin by Atomic Force Microscopy

“…Nucleosomes in the third category ( Figure 3E) appeared to have a diagonal raised ridge running across the core, resembling the front views illustrated by Arents et al (1991). Cores in both the putative axial and front view categories had an average height of 4.4 f 0.9 nm (n = 42), a value consistent with modeled views of the nucleosome and that observed for nucleosomes in the condensed minichromosomes.…”

“…The number of discrete particles observed within partially dissociated nucleosome cores and their dimensions were consistent with their identification as individual histone monomers. Furthermore, the arrangements of these putative histones were consistent with modeled views of the histone octamer based on X-ray crystallography (Arents et al, 1991;Arents & Moudrianakis, 1993).…”

“…Moreover, the resolution obtained in these studies allowed direct visualization of individual histones within partially dissociated nucleosomes. The arrangements of these histone monomers within nucleosomes bore striking resemblance to modeled 3-D views of histone octamers determined by X-ray crystallography (Arents et al, 1991;Arents & Moudrianakis, 1993).…”

“…Although the location of core and linker histones relative to the path of the DNA in the nucleosome has been established (Baldwin et al, 1975;Allan et al, 1980;Richmond et al, 1984;Arents et al, 1991;Arents & Moudrianakis, 1993), the mechanisms by which nucleosomes become compacted into higher order structures have not yet been determined. Several alternative structures have been proposed for the 30 nm chromatin fiber thought to represent the primary level of chromatin folding (Finch & Klug, 1976;Belmont et al, 1989;Wolffe, 1992).…”

Dynamics of interaction of RNA polymerase II with nucleosomes. I. Effect of salts

“…Figure 6 is an attempt to collectively describe all the conformational changes of nucleosomes found in this study through a diagrammatic representation of the histone octamer in the nucleosome (based on the structure given originally by Burlingame et al [1985]). Although these authors have revised their structure, the description of the solvent channels, which forms the basis of the model given in Figure 6, remains unchanged (Arents et al, 1991). When a probe is attached to the cysteines lying at the dyad axis (Fig.…”