Selective recognition of nucleic acids by proteins: the specificity of guanine interaction with carboxylate ions.

The interaction of carboxylate ions (acetate, butyrate) with nucleic aicd bases and nucleosides has been investigated by proton magnetic resonance in dimethyl sulfoxide (d6)/H2O mixtures. Carboxylate ions interacted only with guanine derivatives and led to a large downfield shift of the NH2 resonance. A 1:1 stoichiometry was deduced from a study of the concentration dependence of chemical shifts. A study of substituted guanine showed that hydrogen bonding involved N(1)H and NH2(2). An association constant of 110 M-1 was determined. This value is about 30 times higher than the association constant for guanine-cytosine base pair formation under the same experimental conditions. As a matter of fact, carboxylate ions induced a dissociation of guanine-cytosine base pairs. This guanine-carboxylate association is experimental evidence for a highly specific interaction that could play an important role in protein/nucleic acid recognition.