The structure of ribonucleic acids. 2. The smaller products of ribonuclease digestion

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Abstract
The smaller products of ribonuclease digestion of ribonucleic acids were isolated by a method involving a preliminary chromatographic separation followed by paper electrophoresis. Detailed instructions for the isolation of 15 of the smaller polynucleotides are given and the theory of the separation of polynucleotides by paper electrophoresis discussed. Several dinucleotides were subjected to a degradation process which showed that their general structure is pyrimidine nucleoside 5[image]- (nucleoside-3[image] or 2[image]-phosphate) ester 3[image] or 2[image]-phosphate, or the cyclic form of such a dinucleotide, pyrimidine nucleoside 5[image]-(nucleoside-3[image] or 2[image]-phosphate) ester 2[image], 3[image]-cyclic phosphate. During ribonuclease digestion the cyclic forms of the dinucleotides are first liberated and the 2[image],3[image]-cyclic phosphate link is subsequently slowly hydrolysed by the enzyme to give the 3[image]-(or 2[image]-) phosphates. Trinucleotides liberated by ribonuclease action all have at least one pyrimidine nucleotide residue. The alkali-labile link in ribonucleic acids is at C[image]-5. Ribonuclease hydrolyzes certain esters of pyrimidine ribonucleoside 3[image]-(or 2[image]-) phosphates. Four dinucleoside monophosphates were prepared by hydrolysis with ribonuclease followed by phos-phomonoesterase. A structure for ribonucleic acid was proposed which satisfies these results on the basis of an unbranched chain.