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Probing counterion modulated repulsion and attraction between nucleic acid duplexes in solution.
Yu Bai1, Rhiju Das, Ian S Millett
1Department of Biochemistry, Stanford University, Stanford, CA 94305, USA.
Summary
Counterions do not significantly attract DNA duplexes, even at high concentrations. This study shows that electrostatic repulsion dominates nucleic acid interactions under physiological conditions.
Area of Science:
- Biophysics
- Molecular Biology
- Biochemistry
Background:
- Understanding nucleic acid interactions requires knowledge of surrounding ion atmospheres.
- Processes like DNA condensation and RNA folding are influenced by ions.
- Specific ion-binding sites and complex interactions can complicate these studies.
Purpose of the Study:
- To investigate how ion atmospheres modulate DNA duplex interactions.
- To determine if counterions can reverse Coulombic repulsion into attraction between nucleic acids.
- To assess the significance of counterion-induced attraction under physiological conditions.
Main Methods:
- Utilized a simple model DNA system with two duplexes linked by a flexible, neutral tether.
- Employed small-angle X-ray scattering (SAXS) to determine molecular conformation.
- Tested various cation concentrations (Na+, Mg2+, spermidine3+) to observe effects on DNA duplexes.
Main Results:
- Extended DNA duplexes were observed under low-salt conditions (20 mM Na+) due to Coulombic repulsion.
- High concentrations of Na+, Mg2+, and spermidine3+ led to electrostatic relaxation into a random state.
- No significant counterion-induced attractive force between DNA duplexes was detected under tested ionic conditions.
Conclusions:
- Counterion-induced attraction between nucleic acid duplexes is not significant under physiological conditions.
- Electrostatic repulsion appears to be the dominant force governing interactions between DNA duplexes.
- The study provides an upper limit for the attractive potential under various ionic conditions.