Viscosity as an additional physico-chemical parameter for studying chromatin structure

Area of Science:

• Biochemistry
• Molecular Biology
• Physical Chemistry

Background:

• Chromatin's higher-order structures are complex assemblies of DNA and proteins.
• Understanding chromatin's physical properties is crucial for comprehending its biological functions.

Purpose of the Study:

• To investigate the physico-chemical properties of chromatin, specifically its viscosity.
• To correlate viscosity with other parameters like sedimentation and diffusion coefficients.
• To elucidate the structural dynamics of chromatin in response to varying ionic strengths.

Main Methods:

• Measurement of viscosity values for chromatin in higher-order structures.
• Comparison of chromatin viscosity with isolated DNA.
• Analysis of sedimentation and diffusion coefficients.
• Evaluation of structural changes under different ionic strength conditions.

Main Results:

• Chromatin's higher-order structures exhibit significantly lower viscosity (0.1-0.4 dl/g) compared to isolated DNA.
• Viscosity, sedimentation, and diffusion coefficients are consistent with a compact molecular mass and shape for chromatin.
• Decreased ionic strength leads to increased viscosity and decreased s-value, indicating structural unravelling.

Conclusions:

• Chromatin possesses a compact quaternary structure that unfolds in low ionic environments.
• The observed physico-chemical parameters support a model of chromatin structure that transitions from compact to a less extended tertiary structure.
• Ionic strength is a key regulator of chromatin's structural organization and physical properties.