Sedimentation of DNA in ethanol-water solutions within the interval of B to A transition.

Sedimentation of DNA ethanol-water solutions has been studied over the range of ethanol concentrations corresponding to the B to A transition (65-80% ethanol, v/v). High ethanol concentrations (more than 75%) have been found to promote aggregate formation in solution. The molecular weight of DNA under fixed ionic conditions in solution (5x10(-4)M NaCl) has been shown to influence the value of ethanol concentration at which aggregates appear. On the other hand, the fact that DNA molecular weight has not been found to exert any influence on B to A transition curves obtained from CD measurements suggests that the changes observed in DNA CD spectra on adding ethanol to the solution are independent of aggregate formation. The date obtained show that, first, aggregation is not a necessary condition for the DNA transition from the B to the A-conformation and, second, changes in CD spectra of DNA under the influence of ethanol are not related to the process of aggregation.