Histone hyperacetylation: its effects on nucleosome conformation and stability.

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Histone acetylation is a key epigenetic modification regulating gene expression.
• Butyrate treatment of HeLa cells induces hyperacetylation of histones.
• Nucleosome structure and stability are influenced by post-translational modifications.

Purpose of the Study:

• To investigate the structural and stability differences of nucleosomes with varying levels of histone acetylation.
• To characterize hyperacetylated nucleosomes prepared from butyrate-treated HeLa cells.
• To understand the role of histone acetylation in nucleosome folding at physiological ionic strength.

Main Methods:

• Preparation of nucleosome particles from HeLa cells.
• Fractionation of nucleosomes based on acetylation levels (7-17 acetyl groups per nucleosome).
• Characterization using hydrodynamic behavior, circular dichroism, thermal denaturation, and nuclease sensitivity assays.

Main Results:

• Hyperacetylated nucleosomes showed minimal differences in hydrodynamic behavior and circular dichroism compared to controls at low/physiological ionic strengths.
• Significant differences were observed in thermal denaturation and nuclease sensitivity.
• Hyperacetylated and control nucleosomes exhibited identical stability in high salt concentrations.

Conclusions:

• Highly hyperacetylated nucleosomes remain essentially folded at physiological ionic strength in the absence of other factors.
• Histone acetylation alone does not disrupt the fundamental folded structure of the nucleosome under physiological conditions.
• A model reconciling these findings on nucleosome stability and structure is proposed.