Aggregation of Guanine Oligoribonucleotides and the Effect of Mercuric Salts.

Since the description by Ralph, Connors, and Khorana (1) of the aggregation of deoxyguanylic oligonucleotides, it has been possible to ascribe many observations in the literature to this phenomenon. Sinsheimer (2) noted that guanine oligonucleotides displayed greater hypochromicity than other oligonucleotides, and Michelson (3) actually postulated hydrogen bonding for chemically synthesized polyriboguanylic acid on the basis of titration studies. Ishikura (4) concluded, from gel filtration studies on ribonucleic acid core, that guanine oligonucleotides aggregated and that the binding force was quite strong. He postulated a guanine-guanine bond and noted that xanthylic acid counterparts did not exhibit this behavior. More recently, it has been reported that polyriboguanylic acid (5), enzymatically synthesized oligoribonucleotides (6), and guanosine phosphate itself (7) also form stable secondary structures. This paper presents a detailed description of the aggregates formed by oligoribonucleotides of guanylic acid. A comparison of these structures with those formed by the addition of mercuric salts to the guanine bases in polyguanylates is also made. This comparison is based on spectral changes, behavior to heat, and gel filtration characteristics. The importance of rigorous exclusion of metals from polyguanylate preparations is emphasized.