Protonated polynucleotide structures. Specific complex formation between polycytidylic acid and guanosine or guanylic acids.

Abstract

The interaction between poly(C) and guanylic monomers (guanosine, Guo‐5′‐P, Guo‐3′‐P and Guo‐2′/3′‐P) at millimolar concentrations was investigated by optical methods. All monomers formed complexes of stoichiometry of 1 guanosine for 2 cytidines although under sensibly different conditions: while guanosine, Guo‐3′‐P and Guo‐2′/3′‐P formed complexes stable over several pH units, the interaction between poly(C) and Guo‐5′‐P is only stable within 0.1 pH units. The reasons for this surprising behaviour must be searched for in a conformation of Guo‐5′‐P which differs from the other guanyl monomers. All complexes observed follow cooperative binding. The interactions are only stable in the presence of a large excess of monomer. Nearest neighbour interaction energies computed are found to be between 2 and 3 kcal/mole, sensibly lower than found in polymer interactions. From the results presented it appears that the poly(C)‐guanyl monomer complexes have similar or identical geometry as poly(C) + poly(G) at acid pH.