DIELECTRIC-CONSTANT AND IONIC-STRENGTH EFFECTS ON DNA PRECIPITATION

We have investigated the effect of different zwitterionic compounds on DNA precipitation induced by spermine(4+). Glycine, beta-alanine, 4-a minobutyric acid, and 6-aminocaproic acid have shown an increasing cap acity to attenuate DNA precipitation. This protection effect has been correlated with the dielectric constant increase of their correspondin g solutions. Calculations based on these experimental data and counter -ion condensation theory have confirmed the importance of this paramet er for DNA-ion interactions and precipitation mechanisms. We have also observed a resolubilization of DNA in the presence of 6-aminocaproic acid at high spermine(4+) concentration and in the presence of glycine at high spermidine(3+) concentration. This could be explained by an i ncrease of screening effect with polyamine concentration.