Nucleic Acids Research, 1974, Vol. 1, No. 11 1601-1618
© 1974
Articles |
A conformation change of single stranded polyriboadenyiate induced by an electric field
Max-Planck-Institut für Biophysikalische Chemie, 34 Göttingen-Nikolausberg, Am Faasberg Postfach 968, Germany
Received September 23, 1974. Absorbance measurements performed with high molecular weight poly A at pH 8 show that the degree of single strand stacking present at high ionic strength is reduced at low ionic strengths. The salt dependence of the poly A conformation is assigned to an electrostatic repulsion between subsequent turns of the single strand "helix" structure. - Electric fields of 5 to 80 kV/cm induce an increase in the poly A absorbance consistent with a decrease in the ion concentration in the environment of the polymer. The increase of the absorbance is a linear function of the field strength suggesting that the conformation change is caused by a dissociation field effect. At increasing ionic strength, threshold values of the electric field strength have to be exceeded in order to induce measurable absorbance changes. - The time required for the conformation change decreases from about 2 µsec at 10–4 M ionic strength to about 0.3 µsec at high ionic strengths. At low ionic strengths the ion equilibration may influence the rate limiting step, where as the arrangement of the nucleotide residues into the ordered structure is rate limiting at high ionic strengths.