Nucleic Acid and Protein Conference

Abstract

T HE second Gordon Research Conference on Acids and Proteins was held at New Hampton, New Hampshire, August 2731, 1951.2 Among the eighty-one scientists participating in the conference, twenty-three came from countries outside the United States-namely, England (11), Canada (5), Sweden (3), Denmark, Holland, Italy, and Israel. The international character of the meeting was, in large measure, due to the continued support of the Rockefeller Foundation. The main topies under discussion dealt with nucleic acid structure, physical studies on viruses and virus metabolism, effect of ionizing radiations on biological systems, and protein studies. Twenty-two papers were presented at nine sessions. The first two sessions were devoted to a symposium on the structure of nucleic acids and certain nucleotides. Erwin Chargaff (Columbia University), Maurice Stacey (University of Birmingham), Gerhard Schmidt (Boston Dispensary), Waldo Cohn (Oak Ridge National Laboratory), and Hubert S. Loring (Stanford University) discussed the subject from various points of view. Dr. Chargaff first reviewed previous work of his laboratory on the structure of desoxypentose nucleic acids, which had led to the conclusion not only that the compositions of these compounds deviate in most cases very considerably from that postulated by the classical tetranucleotide hypothesis, but also that they differ from each other in a manner characteristic for the species (but not the tissue) from which they have been isolated. On the other hand, certain remarkable regularities in the relative proportions of the nitrogenous constituents were observed. Thus, all desoxypentose nucleic acids so far examined possess a purine-to-pyrimidine ratio of unity, and the same holds for the ratio of guanine to cytosine. The ATtype contains adenine and thymine, whereas the GCtype contains guanine and cytosine as major components. It was found that all the purines can be removed, yielding polymers composed of pyrimidine nucleotides (apurinic acids). In the instance of pentose nucleic acids (PNA), a branched structure with a polyguanylic acid chain as the backbone was considered. In the subsequent discussion, R. G. Wyatt confirmed Chargaff's general conclusions on the basis of his own analyses. He found that desoxypentose 1 Publication No. 8 of the Department of Biophysics. 2 For a report on the first Nucleic Acid and Protein Conference see E. R. Blout and P. M. Doty, Science, 112, 639 (1950). nucleic acids (DNA) from various animal tissues contain a small amount of 5-methyleytosine, the amount being characteristic of the species serving as the source. In contrast, the DNAs of several insect viruses were found to be free of methylcytosine. The nature of the linkages present in desoxypentose nucleic acids was discussed by M. Stacey, who pointed out that polynucleotide chains may be either straight or branched. They may be ruptured by various means, including ultrasonic waves and ion exchange resins. Upon chain rupture, RCHO-groups are set free, resulting in a positive Feulgen reaction, and the release of purine residues may be followed by the Dische reaction. Steric effects may arise from interaction between base (purine, pyrimidine) groups, leading to a partial stripping of the side branches from the main chain. The possibility of cross-linking by amino and enolic hydroxyl groups was considered. In the discussion, Chargaff pointed out that nucleic acids may also be considered as a form of polysaccharide. DNA, in contrast to PNA, does not appear to be highly branched, and it is possible that links other than phosphoric acid ester bonds are involved in the polymer DNA-structure. Stacey mentioned that D. 0. Jordan's work indicates some degree of branching in DNA. The enzymatic hydrolysis of ribonucleic acids, with particular reference to its bearing on the concepts of their structure, was discussed by G. Schmidt, who employed prostate phosphatase, an enzyme of high activity toward PNA. The hypothesis that PNA consists of a purine polynucleotide and a pyrimidine polynucleotide, which are linked together only at one point, was considered untenable on the basis of the results obtained by the enzymatic hydrolysis of PNA by ribonuclease and phosphatase. The action of ribonuclease leads to the conclusion that the core of PNA consists largely of purine nucleotides. PNA represents a highly branched structure, from which the ribonuclease removes terminal pyrimidine nucleotide residues. Studies on the structure of various nucleotides isolated from nucleic acids were described by W. Cohn and H. S. Loring. Dr. Cohn reported the discovery of new nucleotides from previously known nucleic acids from the work of his group on ion exchange adsorption columns. In addition to the separation of isomeric forms of adenylic, guanylic, cytodylic, and uridylic acids from yeast PNA, a fifth desoxypentose