Structures of poly(dG-dC) and poly(dA-dT) stabilized by anions

Area of Science:

• Molecular Biology
• Biophysics
• Spectroscopy

Background:

• DNA can adopt various structural forms beyond the canonical B-DNA.
• The stability of these alternative DNA structures is influenced by environmental factors like ion concentration and hydration.

Purpose of the Study:

• To investigate the influence of different anions (acetate, sulfate, phosphate) on the structural transitions of poly(dG-dC).Na and poly(dA-dT).Na.
• To determine how hydration levels modulate these anion-induced structural changes.

Main Methods:

• Infrared (IR) spectroscopy was employed to analyze DNA structures.
• Non-oriented gels of poly(dG-dC).Na and poly(dA-dT).Na were studied under varying hydration conditions.
• Sodium salts of acetate, sulfate, and phosphate were used at a concentration of 0.36 mole per mole of nucleotide residue, with NaCl as a reference.

Main Results:

• Poly(dG-dC).Na: Acetate stabilized the B* structure, while sulfate and phosphate induced a transition to the Z-form at lower hydration levels.
• Poly(dA-dT).Na: Acetate showed minimal difference compared to chloride, while sulfate and phosphate promoted the A-form over the B-form at lower hydration.
• Anion-specific stabilization of DNA secondary structures (B*, Z, A) was observed, dependent on hydration.

Conclusions:

• Acetate, sulfate, and phosphate anions exhibit selective stabilization of alternative DNA conformations.
• Hydration is a critical factor in mediating anion-induced DNA structural transitions.
• The findings provide insights into the ion-DNA interactions governing DNA polymorphism.