BIOSYNTHESIS OF NUCLEIC ACIDS 



351 



TABLE I 



Per Cent Renewal of Pyrimidines in the Polynucleotides of the Viscera 

 IN the Rat, from Pyrimidine Nucleosides and Nucleotides" 



Compound administered 



" Nucleosides administered at 0.34 mM. per kg. body wt. per day.** Nucleotides administered at 0.4 mM. 

 per kg. body wt. per day .2' 



These nucleosides and possibly thymine and thymine-4-carboxylic acid^^ 

 are unique in that they are the only compounds that have been found to be 

 specific DNA precursors. 



3. A Summary of Compounds Used as Polynucleotide Precursors 



IN THE Rat 



The exploratory metabolic experiments with a newly prepared labeled 

 compound have almost always involved studies of only the nucleic acids 

 from the pooled viscera of a minimum number of animals. In several cases 

 there are also variations in the size of the administered dose and of times 

 and route of administration, and these facts make detailed comparisons of 

 the degrees of incorporation impractical. In the investigations cited here, 

 analyses of other nucleic acid components, proteins, urinary excretion 

 products, etc., furnished evidence that the compounds are specific precur- 

 sors of the moieties in question. The evidence has all indicated that purines 

 or their derivatives are not precursors of the pyrimidines. Nor are pyrimi- 

 dines or their derivatives precursors of purines, although®* with cytidine-N^* 

 there was some appearance of the nitrogen in the DNA purines, a result 

 which was not obtained-* with cytidylic acid-N^^. The renewals of the 2'- and 

 3'-isomers of the purine nucleotides obtainable from PNA have been found 

 to be essentially the same whether the precursor be phosphate," for- 

 mate®*'®' adenine,** nucleosides,^' or nucleotides,^* except in one uncon- 

 firmed instance with phosphate.^" 



" E. Volkin and C. E. Carter, J. Am. Chem. Soc. 73, 1519 (1951). 



68 J. R. Totter, E. Volkin, and C. E. Carter, J. Am. Chem. Soc. 73, 1521 (1951). 



^^ P. Drochmans, D. H. Marrian, and G. B. Brown, Arch. Biochem. and Biophys. 



39, 310 (1952). 

 '" P. Boulanger and J. Montreuil, Biochim. et Biophys. Acta 9, 619 (1952). 



