Complex Formation between Polycytidylic Acid and Guanine Oligonucleotides.

A study of the characteristics of the guanine-cytosine bond is important to the understanding of its contributions to the secondary structure of nucleic acids. However, such a study is very difficult to carry out with synthetic homopolymers because of the occurrence of stable self-bonded guanine structures (1). It is almost impossible to obtain polyriboguanylic acid (poly Gl) in a single-stranded form at reasonable conditions of temperature and pH (2), but there are a few reports concerning interactions between it and poly C. Radding, Josse, and Kornberg (3) obtained poly dGdC mixtures with variable G : C rat.ios as products of deoxyribonucleic acid polymerase, and Fresco (4) has reported the occurrence of polyribo (G + C) as an intermediary in G + G + C formation. If guanine oligonucleotides are used in place of poly G, however, the interference caused by self-bonding of guanine residues becomes less troublesome and more easily controlled. A preliminary study of the interaction of GpGpGp with poly C has been reported (5). A complex containing equal amounts of guanine and cytosine residues (G + C) was observed; it was stable at room temperature. At low temperatures, another, less stable complex (G + G + C) consisting of two parts of guanine and one of cytosine was formed. The present report extends these observations to other guanine oligonucleotides and also describes a complex with the composition, C + G + C, that can arise under certain conditions2