418 D. M. BROWN AND A. R. TODD 



mitting ready formation of cyclic 2',3'-phosphoryl intermediates in the 

 intercon versions of the 2'- and 3 '-nucleotides, whereas the ^rans-relation- 

 ship between the hydroxy] groups at Cs and Cb prevents the formation of 

 cyclic phosphoryl and other^^ derivatives at these positions. As a corollary, 

 it is evident from the above that the course of hydrolysis of analogous de- 

 rivatives would be expected to be different if sugar residues (e.g., xylofura- 

 nose), in which the stereochemical relationships of the hydroxyl functions 

 were altered, were substituted for ribofuranose in the nucleosides. Ribose 

 and deoxyribose in their furanose forms are uniquely suited for incorpora- 

 tion in the nucleic acids. 



The above observations on the reactions of simple esters of the mono- 

 nucleotides can be applied directly to the elucidation of ribonucleic acid 

 structure. 



3. General Structure of Polyribonucleotides Based on Chemical 



Degradation 



It was early shown that when ribonucleic acids are treated with mild 

 alkaline reagents under a variety of conditions they are rapidly converted 

 to a mixture of their component mononucleotides. "''^^ [Cf. Chapters 5 and 

 11.] Claims to the isolation of larger f ragments^^ '^^ have generally been 

 relinquished or refuted by other workers on the general grounds that the 

 products described were separable mixtures of mononucleotides^^''''® (com- 

 pare, however, Smith and Allen"). In the same way, mild acid hydrolysis 

 also yields mononucleotides, although further degradation of the purine 

 nucleotides complicates the picture. The early observation that the final 

 products of alkaline hydrolysis are mononucleotides has been confirmed by 

 recent studies using chromatographic*^'^*'*" and electrophoretic*^ separation, 



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