Nucleosomes play a dual role in regulating transcription dynamics

Area of Science:

• Molecular Biology
• Biophysics
• Genetics

Background:

• Transcription involves the mechanical movement of RNA polymerase (RNAP) along DNA, coupled to chromatin torsion.
• The precise mechanisms by which chromatin mechanics regulate eukaryotic transcription remain largely unknown.

Purpose of the Study:

• To model the torsional response of topology-constrained chromatin using statistical mechanics.
• To investigate the interplay between DNA supercoiling, nucleosome dynamics, and RNAP translocation.
• To elucidate the dual role of nucleosomes in regulating transcription dynamics.

Main Methods:

• Statistical mechanics modeling of chromatin's torsional response.
• Stochastic simulations coupling chromatin mechanics with RNAP translocation.
• Comparison of model predictions with experimental data from budding yeast.

Main Results:

• Chromatin exhibits weaker torsional stiffness than bare DNA, driven by nucleosome structural transitions.
• Nucleosomes act as steric barriers but also facilitate RNAP motion through chiral transitions.
• Highly dynamic nucleosomes enhance transcription elongation by buffering DNA twist, particularly in weakly transcribed genes.
• Model predictions for transcription-dependent DNA supercoiling in yeast align with experimental data.

Conclusions:

• Nucleosome dynamics and DNA supercoiling are critical regulators of transcription elongation.
• A paradigm of DNA supercoiling-mediated gene interactions is proposed.
• The study provides testable predictions to guide future experimental research in transcription regulation.