Torque and buckling in stretched intertwined double-helix DNAs

Area of Science:

• Statistical mechanics
• Biophysics
• Molecular biology

Background:

• Intertwined DNA structures exhibit complex mechanical properties.
• Understanding DNA behavior under force is crucial for molecular biology and nanotechnology.

Purpose of the Study:

• To develop a statistical-mechanical model for intertwined DNA behavior.
• To analyze the influence of catenation and applied force on DNA torque and extension.
• To compare model predictions with experimental data from magnetic tweezers.

Main Methods:

• Statistical-mechanical modeling of DNA.
• Analysis of torque and extension as functions of linking number and applied force.
• Comparison with magnetic tweezers experimental data.

Main Results:

• The model accurately predicts experimental data for intertwined DNA.
• A distinct, catenation-dependent effective twist modulus was predicted.
• Buckling and a "supercoiled braid" state with multiple plectonemes were identified.
• A predicted extension discontinuity at buckling corresponds to plectoneme nucleation.

Conclusions:

• The statistical-mechanical model provides insights into intertwined DNA mechanics.
• Buckling behavior in intertwined DNA differs significantly from single DNA molecules.
• Environmental factors like salt concentration influence buckling differently in intertwined DNA.