WALDO E. COHN 



tions of the group transfer activities of guanosine diphospho- 

 mannose (50) and of cytidine diphosphocholine (37) extend the 

 Hst of functional examples of this type of compound from uridine 

 diphosphate derivatives (12,13,21,36,42,61) and the well-known 

 adenosine coenzymes to include at least one representative of 

 each of the four RNA bases. The coenzyme and carrier functions 

 of some of these substances were revealed because modern 

 chromatography made available more highly purified adenosine 

 phosphates, thus exposing the role previously played by an 

 impurity (examples of this type of discovery are : ( 7) guanosine 

 triphosphate in the succinyl-coenzyme A reaction (53), and in 

 amino acid incorporation in vitro (65) ; (2) cytidine diphospho- 

 choline in lecithin synthesis (38)). Others have been shown to 

 be substrates for enzymic oxidations or other conversions 

 (12,21,36,61). The possibility that compounds of this type are 

 precursors of RNA, or are in equilibrium with such precursors, 

 is indicated by studies of the rate of incorporation of labeled 

 precursors (32) and by the recent observation of the enzyme- 

 catalyzed polymerization of nucleoside diphosphates into 

 polynucleotide structures and the depolymerization (phosphor- 

 olysis) of RNA into the diphosphates (24) . The latter is a method 

 of synthesis of polynucleotide material considerably different 

 from that involving the reverse of ribonuclease degradation of 

 RNA involving cyclic pyrimidine nucleotides (31), although 

 both involve diesterified phosphate groups. Nor should other 

 5' nucleotide precursors, ribose 1 -pyrophosphate 5-phosphate 

 (41,52) and the two glycineamideribose 5 '-phosphates (23,28), 

 also isolated by ion-exchange chromatography, be overlooked 

 in this listing. 



From all of this there arises the concept of coenzymes and 

 transfer agents involving all of the RNA nucleoside 5 '-phosphates, 

 these being in metabolic equilibrium with RNA and also possible 

 precursors, with respect to the phosphodiester linkage, of RNA. It 

 thus becomes possible to consider RNA as a source of coenzymes, 

 or carriers, a possible new function to go with the new structure. 

 Whether this relationship of RNA to intermediary metabolism 



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