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Stretching single-stranded DNA: interplay of electrostatic, base-pairing, and base-pair stacking interactions.
1Institute of Theoretical Physics, The Chinese Academy of Sciences, Beijing 100080, China. yzhang@danforthcenter.org
Biophysical Journal
|July 21, 2001
Summary
Single-stranded DNA (ssDNA) elasticity depends on ion concentration and sequence. Our model shows electrostatic forces dominate in low salt, while base-pairing and stacking drive hairpin formation and transitions in high salt.
Area of Science:
- Biophysics
- Molecular Biology
- Computational Chemistry
Background:
- Single-macromolecule experiments show ssDNA force/extension properties vary with ionic concentration and sequence.
- Understanding these relationships is crucial for predicting ssDNA behavior in different environments.
Purpose of the Study:
- To investigate the elastic properties of single-stranded DNA (ssDNA).
- To model the influence of electrostatic interactions, base-pairing, and base-pair stacking on ssDNA elasticity.
Main Methods:
- Utilized Monte Carlo simulations with a modified freely jointed chain (FJC) model.
- Incorporated electrostatic, base-pairing, and base-pair stacking interactions into the simulations.
Main Results:
- Simulated force-extension profiles accurately matched experimental data for random and designed ssDNA sequences.
- In low salt, electrostatic interactions dominate, facilitating molecule alignment.
- In high salt, hairpin structures form, leading to continuous hairpin-coil transitions in random sequences and discontinuous transitions in designed sequences (e.g., poly(dA-dT), poly(dG-dC)) due to base-pair stacking.
Conclusions:
- ssDNA elasticity is significantly influenced by ionic strength and sequence composition.
- Base-pairing rules favor nested, independent planar hairpin structures over random intersecting patterns in ssDNA.