Viscosity of chromatin solutions increases with increasing ionic strength

Area of Science:

• Biochemistry
• Molecular Biology
• Chromatin Structure

Background:

• Chromatin, the complex of DNA and proteins that forms chromosomes, plays a crucial role in genome organization and regulation.
• Understanding chromatin's structural dynamics under varying conditions is essential for comprehending gene accessibility and cellular processes.

Purpose of the Study:

• To investigate the effects of increasing ionic strength on the structural organization and physical properties of rat liver chromatin.
• To identify the specific histone proteins involved in chromatin structural transitions at different ionic strength levels.

Main Methods:

• Preparation of rat liver chromatin solutions.
• Measurement of solution viscosity at increasing ionic strengths (0.4 M to 0.7 M).
• Analysis of histone dissociation and chromatin structural changes in response to ionic strength variations.

Main Results:

• Chromatin solution viscosity increases significantly above 0.4 M ionic strength, indicating a transition from compact to elongated forms.
• Histone H1 dissociates between 0.4 M and 0.5 M ionic strength, leading to the unraveling of chromatin's quaternary structure.
• Above 0.5 M, further viscosity increases are observed due to structural deformation, with core histones H2A and H2B beginning to dissociate near 0.7 M, causing nucleosome core opening and increased molecular elongation.

Conclusions:

• Ionic strength is a critical factor modulating chromatin structure and stability.
• The sequential dissociation of histone H1 and core histones at specific ionic strengths drives significant structural changes in chromatin, impacting its physical properties and molecular organization.