Oscillatory pattern of chain extension and nucleosome self-association with variation in protein-free DNA linker length in simulated nucleosome-decorated DNA chains. Regular structures bearing 15 nucleosomes constructed from the mean rigid-body parameters between successive base pairs; nucleosomal cores depicted as wedge-shaped objects and color-coded to highlight the two- and three-start organization of the structures. Nucleosomal DNA constrained to the 147-bp pathway found in the best-resolved core particle structure, pdb_id 1kx5
Distortions in the average structures of simulated nucleosome-decorated DNA chains introduced by changes in the positioning of a singe nucleosome. A. Local opening and unpacking of a compact array introduced by a single 2-bp increment in the spacing between nucleosomes. B. Kinking of an extended array by a single 5-bp increment in nucleosome spacing.
Effects of the nucleosomal DNA pathway on the average configurations of simulated 12-nucleosome arrays. Average structures bearing the undertwisted DNA found in the best-resolved core particle structure, pdb_id 1kx5, compared to the overtwisted DNA found in the RCC1-nucleosome complex, pdb_id 3mvd. The regulatory protein is not included in the simulations. Upper views looking perpendicular to the chromatin axis and lower views down the axis
Molecular 'snapshots' illustrating the potential effects of chain length and nucleosome positioning on large-scale chromatin folding. A. Smoothly deformed array of 78 nucleosomes with uniform 177-bp spacing. B. 77-nucleosome chromatin 'copolymer' containing three stretches of nucleosomes with different spacings: a compact array of 26 nucleosomes (deep brown) with 172-bp spacing at the 5́-end of the chain; an extended array of 26 nucleosomes (light brown) with 177-bp spacing in the middle; an opened array of 25 nucleosomes (yellow) with 207-bp spacing and a nucleosome-free gap at the 3́-end of the chain. Note the more pronounced junction between ‘helical’ stretches when the spacing changes by roughly a half turn of DNA (172 – 177 = –5 bp) than when altered by a multiple of the double-helical repeat (207 – 177 = 30 bp). The presence of a nucleosome-free gap, within the stretch of nucleosomes spaced at 207-bp intervals, enhances the flexibility of the modeled structure, allowing the chain to bend in various directions
Contributions of local structural and energetic features of DNA to large-scale genomic organization [perspective by Wilma Olson & Co) www.sciencedirect.com/science/arti...
