The structure of ribonucleic acid. 3. The end groups, the general structure and the nature of the ‘core’

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Abstract
Two methods were developed for the identification of nucleotides which occupy end positions in ribonucleic acid chains and bear terminal phosphoryl groups. The cyclic nucleotides adenosine 2[image],3[image]-monohydrogen phosphate and guanosine 2[image],-3-monohydrogen phosphate, and adenylic, guanylic, cytidylic and uridylic acids were recognized as end groups in the ribonucleic acids of yeast and turnip yellow mosaic virus. Estimates were made of the proportions of these terminal groups present in the 2 nucleic acids. It is concluded that ribonucleic acid consisists of mixtures of many kinds of comparatively short chains. The frequencies with which the nucleotides occur among the ribonuclease-resistant digestion products was studied. The distr. of cytidylic and uridylic acids among the positions occupied by the pyrimidine nucleotides in the intact nucleic acid chain appears to be random. That of guanylic and adenylic acids, however, is not random. The "core" of ribonucleic acids, that is, the fraction of the ribonuclease digest which does not dialyse into water through cellophane film, was shown to be readily dialysable against salt solns. It is a mixture of polynucleotides about 3-5 residues in length and each polynucleotide is a chain of purine nucleotides terminated by a phosphoryl group on C atom 2[image] or 3[image]. The components of the core have the same structure as the other ribonuclease-resistant polynucleotides.