Conformational statistics of non-equilibrium polymer loops in Rouse model with active loop extrusion

Area of Science:

• Polymer Physics
• Molecular Biophysics
• Biophysics

Background:

• Recent experiments show protein motors extruding DNA loops.
• Understanding the statistical properties of these extruded loops is crucial.

Purpose of the Study:

• Investigate statistical properties of growing polymer loops formed by DNA extrusion.
• Analyze how loop conformation is affected by extrusion dynamics.

Main Methods:

• Utilized the ideal chain model for polymer loops.
• Employed rigorous semi-analytical methods.
• Performed asymptotic analysis for slow and fast extrusion limits.

Main Results:

• A single dimensionless parameter (loop relaxation time / elapsed extrusion time) controls loop statistics.
• This parameter governs the crossover between equilibrium and non-equilibrium regimes.
• One-sided and two-sided motors yield nearly identical loop properties.

Conclusions:

• The dynamics of DNA loop extrusion can be universally described by a key dimensionless parameter.
• Extrusion velocity's time dependence does not alter fundamental loop statistics.
• The findings provide a theoretical framework for understanding DNA loop extrusion in biological systems.