BIOSYNTHESIS OF NUCLEIC ACIDS 345 



an experiment in which the PNA and DNA were separated, little incorpora- 

 tion of adenine into DNA was detected.^* However it was later demon- 

 strated that adenine is utilized for DNA synthesis in rapidly growing tissues, 

 for example, intestine'^ -^^ and regenerating liver." In all species sub- 

 sequently tested, adenine has proved to be moderately to extensively in- 

 corporated into the polynucleotides, and in most instances it is also con- 

 verted into polynucleotide guanine. 



In an experiment in which yeast nucleic acid uniformly labeled with 

 ]N^i5 18 ^yg^g hydrolyzed by alkali, presumably to a mixture of mononucleo- 

 tides, and this was injected into rats at a level of 0.4 mM. per kilogram of 

 body weight per day, it was found that only 3.7 % of both adenine and gua- 

 nine of the visceral nucleic acids had been derived from the labeled com- 

 pounds.^" Thus it is evident that free adenine is a much better precursor of 

 nucleic acids than is combined adenine. This was further demonstrated in 

 an experiment by Lowy et al}^ in which adenosine-8-C^^ ^^ was administered 

 to rats at the 0.2-mM. level and was found to be incorporated into PNA 

 and DNA adenine about only one-half as well as was adenine. 



Adenylic acid uniformly labeled with N^^ was isolated from labeled yeast 

 nucleic acid,'^ and when injected into rats at twice the level at which adeno- 

 sine was given was found^^ to be incorporated to only twice the extent, which 

 indicated that it too was a less effective precursor than was adenine. This 

 was later confirmed in experiments in which the 2'- and S'-isomers'^^ of ade- 

 nylic acid-8-C^'* were administered^^ separately to rats at the same level as 

 was adenosine. It was found that the adenylic acids were incorporated to 

 approximately the same extent as was adenosine and also that each isomer 



1^ G. B. Brown, M. L. Petermann, and S. S. Furst, /. Biol. Chem. 174, 1043 (1948). 

 *^ R. Abrams, Arch. Biochem. and Biophys. 33, 436 (1951). 

 »« D. A. Goldthwait and A. Bendich, J. Biol. Chem. 196, 841 (1952). 

 " S. S. Furst, P. M. Roll, and G. B. Brown, /. Biol. Chem. 183, 251 (1950). 

 18 The nucleic acid was isolated from yeast which had been grown in a medium con- 

 taining (N>6H4)2S04 .'^ 



1" F. J. DiCarlo, A. S. Schultz, P. M. Roll, and G. B. Brown, J. Biol. Chem. 180, 329 



(1949). 

 20 P. M. Roll, G. B. Brown, F. J. DiCarlo, and A. S. Schultz, J. Biol. Chem. 180, 333 



(1949). 

 " B. A. Lowy, J. Davoll, and G. B. Brown, /. Biol. Chem. 197, 591 (1952). 

 ^'^ Synthesized via a labeled purine and chloroacetoribofuranose.^' 

 " J. Davoll and B. A. Lowy, /. Am. Chem. Soc. 74, 1563 (1952). 

 " P. M. Roll and L Weliky, Federation Proc. 10, 238 (1951). 

 '^ Yeast was grown in a medium containing adenine-8-Ci'' ^^ and, from the nucleic 



acid, purine nucleotides were isolated by ion-exchange procedures.^' 

 2« S. E. Kerr, K. Seraidarian, and G. B. Brown, /. Biol. Chem. 188, 207 (1951). 

 " W. E. Cohn, /. Am. Chem. Soc. 72, 1471 (1950). 

 28 G. B. Brown, P. M. Roll, and H. Weinfeld, in "Phosphorus Metabolism" (McElroy 



and Glass, eds.), Vol. 2, p. 385. Johns Hopkins Press, Baltimore, 1951. 



