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Unfolding of 175-base-pair nucleosomes
Biochemistry
|February 16, 1982
Summary
Calf thymus nucleosomes with 175 base pairs of DNA show two unfolding steps as salt concentration decreases. These structural changes, observed via electric dichroism, reveal distinct disklike and elongated forms at specific ionic strengths.
Area of Science:
- Molecular Biology
- Biophysics
- Structural Biology
Background:
- Nucleosomes are the fundamental units of DNA packaging in eukaryotes.
- Understanding nucleosome structure and dynamics is crucial for gene regulation.
Purpose of the Study:
- To investigate the salt-induced unfolding transitions of calf thymus nucleosomes containing 175 base pairs of DNA.
- To characterize the structural intermediates formed during nucleosome unfolding.
Main Methods:
- Electric dichroism measurements were employed to monitor nucleosome unfolding.
- Experiments were conducted at low temperatures (7 degrees C) across varying salt concentrations.
Main Results:
- Nucleosomes exhibited two distinct unfolding steps, with transition midpoints at 2.9 mM and 1.1 mM ionic strength.
- The 2.9 mM transition yielded an expanded disklike structure, similar to that observed in 146-base-pair nucleosomes.
- The 1.1 mM transition resulted in a more elongated and asymmetric particle structure.
Conclusions:
- Calf thymus nucleosomes undergo a two-step unfolding process dependent on salt concentration.
- The observed structural transitions provide insights into the stability and conformational flexibility of nucleosomes.