The effect of polyols on the stability of duplex DNA

It has been observed that double stranded DNA in solution is thermally destabilized by the presence of several organic molecules, among which are alcohols and polyols. This finding, and the fact that sugar moieties are components of some nuclear proteins and DNA binding drugs, may suggest a role for oligosaccharides in DNA recognition and/or interaction. In order to investigate this possibility, the effect of several sugars and other polyols on the thermal stability and on the conformation of DNA has been studied by high sensitivity differential scanning calorimetry and circular dichroism. While addition of small size polyols does not influence appreciably the melting enthalpy, it always results in a decrease in the DNA melting temperature. The magnitude of the destabilizing effect depends on the concentration of additives, reaching 13.5 degrees C in 50% (5.4M) glycerol. It also depends on the nature of the additives, e.g., sorbitol is more efficient than inositol, while dextran has no effect on the DNA melting temperature. According to circular dichroism results, DNA undergoes a significant structural change in the presence of small sugars or polyols: a continuous loss in 'B' character is observed as the glycerol concentration is gradually increased. This conformation change appears to be related to the decrease in thermostability.