CONFORMATION STATE OF POLY[D(I-C)].POLY[D(I-C)] MOLECULES IN AQUEOUS-SOLUTIONS

The conformation and thermostability of poly[d(I-C)].poly[d(I-C)] were studied by the methods of absorption spectroscopy, fluorescence, circular dichroism and by analyzing the characteristics of ethidium bromide interaction with the polynucleotide. Calculation showed that the saturation stoichiometry corresponded to one ethidium bromide molecule per three polynucleotide bases with a binding constant of (2.5 +/- 0.2) x 10(5) M-1 at 25-degrees-C and 0.1 M NaCl. Under physiological conditions poly[d(I-C)].poly[d(I-C)] formed right helices, but different from the B-form, and did not pass into the left-helical form when the NaCl concentration raised to 5 M. The CD spectra changed continuously with the increasing concentrations of salts and alcohols, this being evidence of an interfamiliar conformational transition.