A comparison of the binding to polynucleotides of complementary and noncomplementary oligonucleotides.

The binding of oligonucleotides to synthetic polynucleotides has been studied as a control for investigations of the binding of oligonucleotides to natural RNA molecules. Only combinations that involved A-U, G-C, and G-G pairs were found to be significantly stable under the experimental conditions used here. The stability of the oligomerpolymer pairing increased with the length of the region paired and with its G + C content. Further, some different sequence isomers of the same G + C content exhibited quite different binding constants. This variability is consistent with certain sequence differences in the double-strand stacking interactions stabilizing the oligomer-polymer association. Oligomer binding was also shown to depend upon the identity of the polymer residues neighboring the binding site, indicating the effect upon oligomer binding of small changes in the single-strand conformation of the binding site. These observations validate the criteria that allow one to decide if an observed association constant of an oligomer to an RNA molecule reflects a complete complementarity between the two or not. This improves the basis for using oligonucleotide binding constants to RNA of known sequences to map secondary structure.