Nucleosomes structure and dynamics: effect of CHAPS

Area of Science:

• Chromatin biology
• Molecular biophysics
• Biochemistry

Background:

• Nucleosome dynamics and DNA unwrapping are crucial for gene regulation.
• Single-molecule techniques are vital for studying these dynamics.
• Nucleosome dissociation at low concentrations complicates these studies.

Purpose of the Study:

• To evaluate the efficacy of CHAPS (3-[(3-Cholamidopropyl)dimethylammonio]-l-propanesulfonate) in preventing nucleosome dissociation.
• To assess the impact of CHAPS on nucleosome conformation and stability.

Main Methods:

• Assembly of mononucleosomes using human histones and the 601 DNA sequence.
• Atomic Force Microscopy (AFM) for direct visualization and structural analysis of nucleosomes.
• Incubation of nucleosomes with varying concentrations of CHAPS and NaCl.

Main Results:

• Millimolar concentrations of CHAPS prevent nucleosome dissociation for days, even at sub-nanomolar concentrations.
• AFM confirmed that CHAPS does not alter nucleosome conformation.
• CHAPS (16 µM) stabilizes nucleosomes for over an hour at 0.4 nM concentrations.
• Nucleosome stability decreased at physiological salt concentrations (150 mM NaCl) and rapidly dissociated at 300 mM NaCl.
• CHAPS reduced sequence specificity, suggesting histone core translocation via sliding.

Conclusions:

• CHAPS is an effective agent for stabilizing nucleosomes, overcoming dissociation issues in low-concentration single-molecule experiments.
• The use of CHAPS allows for extended observation of nucleosome dynamics without conformational changes.
• CHAPS facilitates the study of nucleosome-DNA interactions, including histone core sliding mechanisms.