Transcription dynamics stabilizes nucleus-like layer structure in chromatin brush.

Area of Science:

• Biophysics
• Molecular Biology
• Genomics

Background:

• Chromatin structure is crucial for gene regulation.
• Nucleosome dynamics, including disassembly and reassembly, are fundamental to transcription.
• Phase separation is increasingly recognized as a mechanism for organizing cellular components.

Purpose of the Study:

• To theoretically predict the phase separation behavior of DNA brushes in the presence of transcriptional machinery and histone proteins.
• To elucidate the relationship between DNA brush structure, nucleosome occupancy, and transcriptional activity.
• To explore the potential implications of these findings for understanding chromatin organization in different cell types.

Main Methods:

• Theoretical modeling of DNA brushes under conditions simulating transcription.
• Analysis of phase separation phenomena based on polymer physics principles.
• Investigation of the role of nucleosome occupancy and histone proteins in driving structural transitions.

Main Results:

• DNA brushes undergo phase separation into collapsed and swollen chain layers, mimicking chromatin organization.
• The observed layer structure is stabilized by the lateral osmotic pressure of swollen chains.
• Tricritical points are identified at low grafting densities, associated with significant fluctuations in local nucleosome concentration.

Conclusions:

• Transcription-induced nucleosome instability drives phase separation in DNA brushes.
• The resulting layered structure provides a theoretical model for chromatin organization in differentiated cells.
• Fluctuations at tricritical points may offer insights into chromatin dynamics in embryonic stem cells.