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#chromatosome

3 public questions tagged with this topic.

Nucleosome Packing

Total DNA length in a chromatosome is approximately:

Chromatosome differs from nucleosome core particle by retention of linker histone H1 and extra protected DNA length. Core particle with octamer protects 147 base pairs, but complete chromatosome containing H1 protects additional twenty base pairs, ten on each side beyond core entry, totaling 167 base pairs. Measurement obtained by micrococcal nuclease digestion followed by DNA sequencing of protected fragments when H1 retained; extensive digestion removes H1 reducing fragment to 147 base pairs core. Universally reported value 167 base pairs defines functional unit before 30 nanometer fiber for

Ref: Simpson RT 1978 J Biol Chem 273; NCBI Bookshelf, Chapter 4: Chromatosome 167 bp Total Length

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Nucleosome Packing

Linker histone associated with chromatosome is:

Linker DNA connecting adjacent nucleosomes constitutes binding site for fifth histone family distinct from core. H1 binds at dyad axis where DNA enters and exits octamer, globular winged-helix domain contacts both linkers while lysine-rich C-terminal tail neutralizes linker DNA charge. Interaction seals nucleosome, determines exit angle and promotes 30 nanometer fiber folding into solenoid or zigzag conformations. Core histones H2A, H2B, H3 remain buried inside octamer forming handshake motifs, not contacting linker extensively. Therefore H1 classifies as linker histone easily extracted at mod

Ref: Allan et al., J Mol Biol 1980; Alberts et al., Molecular Biology of the Cell, Chapter 4: Linker Histone H1 Chromatosome

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Eukaryotic chromatin and chromosome

Chromatosome includes:

Limited nuclease digestion in presence of H1 yields larger protected fragment than core alone. Chromatosome comprises nucleosome core particle of 147 base pairs wrapped around octamer plus additional twenty base pairs of linker DNA, ten on each side of entry exit, sealed by globular winged-helix domain of histone H1 contacts. Total DNA content becomes about 167 base pairs, determined by sequencing H1-containing fragments. Structurally H1 locks DNA crossover angle, directing trajectory of adjacent linkers for higher-order folding and reducing entry-exit breathing. Chromatosome represents comple

Ref: Simpson RT 1978 J Biol Chem; Alberts et al., Molecular Biology of the Cell, Chapter 4: Chromatosome Core plus H1 167 bp

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