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Updated: Aug 3, 2026
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Assembly of Nucleosomal Arrays from Recombinant Core Histones and Nucleosome Positioning DNA
Published on: September 11, 2013
Removal of histone H1 exposes a fifty base pair DNA segment between nucleosomes
Biochemistry
|July 27, 1976
Abstract:
Micrococcal nuclease has been used to prepare chromatin from HeLa cells and to probe the structure of HeLa chromatin under various ionic conditions and after the removal of chromatin proteins by salt extraction. The results suggest that (1) HeLa chromatin DNA exists as 150-160 base pair beads interspersed with 40-50 base pair bridges;(2) the bead and bridge conformation exists at physiologic salt concentrations; and (3) removal of histone H1 renders the 40-50 base pair bridge, but not the 150-160 base pair bead, more nuclease susceptible.
Insights
HeLa cell chromatin DNA forms 150-160 base pair beads and 40-50 base pair bridges at physiological salt concentrations. Removing histone H1 increases nuclease susceptibility of the DNA bridges.
Area of Science:
- Molecular Biology
- Chromatin Structure
- Biochemistry
Background:
- Chromatin is the complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells.
- Understanding chromatin structure is crucial for comprehending DNA packaging, gene regulation, and cellular processes.
- Micrococcal nuclease is a widely used enzyme for probing DNA accessibility within chromatin.
Purpose of the Study:
- To investigate the structural organization of HeLa cell chromatin.
- To determine the effect of ionic conditions and protein removal on chromatin structure.
- To elucidate the role of histone H1 in maintaining chromatin conformation.
Main Methods:
- Preparation of chromatin from HeLa cells using micrococcal nuclease.
- Analysis of chromatin structure under varying ionic strengths.
- Salt extraction to remove chromatin proteins, followed by nuclease digestion.
- Assessment of DNA fragment sizes to infer structural elements.
Main Results:
- HeLa chromatin DNA is organized into repeating units of 150-160 base pair 'beads' and 40-50 base pair 'bridges'.
- This bead-and-bridge conformation is maintained at physiological salt concentrations.
- Removal of histone H1 by salt extraction significantly increased the nuclease susceptibility of the DNA bridges, but not the beads.
Conclusions:
- HeLa chromatin exhibits a beaded structure with DNA linkers at physiological conditions.
- Histone H1 plays a role in protecting the DNA bridges from nuclease degradation.
- The findings provide insights into the higher-order structure of chromatin and the function of histone H1.
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