A VIBRATIONAL SPECTROSCOPIC STUDY OF THE SELF-ASSOCIATION OF POLYINOSINIC ACID AND POLYGUANYLIC ACID IN AQUEOUS-SOLUTION

We have studied by Raman and ir spectroscopy the structure of self-associated polyinosinic acid and polyguanylic acid in aqueous solution. The results are consistent with the formation of a four-stranded complex, which melts cooperatively near 60-degrees-C in the case of poly (I) in the presence of K+ ions. The conformation of the ribose in both systems is mixed C2'-endo/C3'-endo, giving a structure that is intermediate between the extremes proposed previously from x-ray diffraction studies. Characteristic Raman bands for the C2'-endo ribose conformation in polyribonucleotides are identified. The four-stranded structure of poly (I) appears to be very flexible, with almost-equal-to 15% of the tetrameric segments being disrupted and almost-equal-to 30% of the ribose units adopting a disordered conformation prior to melting. This disordering process increases to almost-equal-to 75% above the melting transition, with the remaining almost-equal-to 25% of the ribose units keeping an ordered C2'-endo or C3'-endo conformation. (C) 1994 John Wiley & Sons, Inc.