Diffusion of DNA-Binding Species in the Nucleus: A Transient Anomalous Subdiffusion Model

Area of Science:

• Biophysics
• Molecular Biology
• Cellular Dynamics

Background:

• Single-particle tracking experiments monitor DNA-binding species (CRISPR-Cas9, TetR, LacI) in living cells.
• Observed escape time distributions follow a truncated power law, inconsistent with Gaussian binding energy models.

Purpose of the Study:

• To model the diffusion dynamics of DNA-binding species.
• To relate escape time distributions to anomalous subdiffusion parameters.
• To explore implications for DNA search kinetics and cellular biophysics.

Main Methods:

• Utilized single-particle tracking experiments to measure escape times.
• Employed Monte Carlo simulations to characterize time-dependent diffusion coefficient D(t).
• Analyzed parameters including anomalous exponent α, crossover time t_cross, and diffusion limits D(0) and D(∞).

Main Results:

• The escape time distribution suggests transient anomalous subdiffusion.
• Diffusion is anomalous at short times and normal at long times.
• Non-target DNA sites and binding/obstruction significantly impact search kinetics.

Conclusions:

• The initial anomalous diffusion phase reflects the search for target DNA sequences.
• False positives on non-target DNA can be rate-determining in vivo.
• The model offers a coarse-grained description for larger-scale kinetic modeling.