Structure of Polynucleotide Complex with Non-Complementary Nucleosides. I. Poly A,G+Poly U

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Abstract
Copolymers of riboadenylic and riboguanylic acids (poly A,G) with guanylic acid contents of 8.5–29.6% were prepared. The ultraviolet and infrared absorptions were examined of aqueous solutions of mixtures of poly A,G and polyribouridylic acid (poly U) of various mole ratios. It has been shown that in a solvent with 0.1 m Na+ a triple-helical structure is formed with a (Remark: Graphics omitted.) type inter-base binding as well as a double-helical structure with a A···U type binding, while in a solvent with 0.01 M Na+ only double-helical structure is formed. A guanine residue in the copolymer remains within the helix structure when its neighbors are mostly adenine residues, whereas it rotates out when there are many guanine residues in its vicity. On heating the solution, the structures just mentioned were found to be broken. The process of such a breaking down was followed also by means of the ultraviolet and infrared absorption measurements.