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Titration of poly(dA-dT) . poly(dA-dT) in solution at variable NaCl concentration
Marta Airoldi1, C Andrea Boicelli, Fabio Cadoni
1Dipartimento di Chimica Inorganica e Analitica S. Cannizzaro, Viale delle Scienze, Università di Palermo, 90128 Palermo, Italy.
Biopolymers
|September 10, 2004
Summary
High molecular weight poly(dA-dT) . poly(dA-dT) undergoes reversible acid- or base-induced transitions between B-double helix and random coil or single strands, respectively. These DNA transitions are influenced by salt concentration and counterion condensation effects.
Area of Science:
- * Biophysics
- * Molecular Biology
- * Polymer Science
Background:
- * High molecular weight poly(dA-dT) . poly(dA-dT) is a synthetic DNA polymer.
- * Understanding DNA structural transitions is crucial for molecular biology and biophysics.
Purpose of the Study:
- * To investigate the acid- and base-induced transitions of poly(dA-dT) . poly(dA-dT).
- * To analyze the reversibility and factors influencing these DNA structural changes.
Main Methods:
- * Circular Dichroism (CD) spectroscopy.
- * UV absorption spectroscopy.
- * Titration experiments in varying NaCl concentrations.
Main Results:
- * Acid-induced transition from B-double helix to random coil observed in NaCl solutions (0.005–0.600M).
- * Base-induced transition from duplex to single strands observed.
- * Transitions were reversible, with apparent pKa values consistent in both directions.
- * Excess protons/hydroxide ions required for half-denaturation, explained by counterion condensation and charge screening effects.
Conclusions:
- * Poly(dA-dT) . poly(dA-dT) exhibits pH-dependent structural transitions.
- * Counterion condensation theory and electrostatic interactions play significant roles in DNA stability and transitions.
- * The findings provide insights into the behavior of DNA under varying ionic and pH conditions.