Conformational study of poly(dI-dC): Hydrogen-deuterium exchange and low-frequency resonance Raman spectroscopy

Poly(dI-dC) structures in aqueous solutions at different salt conditions were studied by classical Raman spectroscopy monitoring the hydrogen-deuterium (H-D) exchange kinetics in 8-CH group in inosine, and by low-frequency (LF) Raman spectroscopy. It is shown that: (i) the Raman spectrum of the low-salt poly(dI-dC) corresponds to the B conformation of the polynucleotide while the isotopic exchange suggests that this form contains a Small portion of the A form, (ii) the high-salt poly(dI-dC) spectrum corresponds to the right-handed polymer with characteristics of both the A and B conformations and the H-D exchange indicates a dominant presence of the A form, and (iii) the LF spectra of the high-salt poly(dI-dC) contain the same features as observed in its low-salt B form and some new peaks which can be attributed to the A form. We conclude that the unusual so-called "X" form of the high-salt poly(dI-dC:) is a mixture of the A and B forms with the A form being predominant. (C) 1999 Elsevier Science B.V. All rights reserved.