Species 

 TorulopBts utilis 

 Aerobacter aerogenes 



Paramecium aurelia (51-K) 

 P. aurelia (51-7SB) 

 Ochromonas rruilhamensis 

 Escherichia coli, B 

 Lactobacillus casei 

 L. casei (mutant) 

 Tetrahymena geleii 

 Lactobacillus leichmanii (313) 



BIOSYNTHESIS OF NUCLEIC ACIDS 



Conversions of Administered Purines 



355 



u 



■■ Conversion of adenine into polynucleotide guanine 

 I I Conversion of guanine into polynucleotide adenine 



Fig. 2. Variations in the interconversions of administered purines by various 

 species. 



The lengths of the bars signify the amount of the polynucleotide purine which 

 arises through conversion as a proportion of that arising through direct incorpor- 

 ation. 



polynucleotide adenine to a degree quite similar to the conversions observed 

 for guanine in the respective species. 



When 2,6-diaminopurine is present with either or both of the other purines, it is 

 transformed equally into each of the polynucleotide purines by L. casei,*" and in mix- 

 tures of any two or three of the purines each is used to an extent approximately 

 proportionate to its concentration. 



There are instances where exogenous adenine or guanine is converted into the poly- 

 nucleotide derivative of the other to a greater extent than it is incorporated per se. 

 For example a haploid Saccharoniyces cerevisiae^'' can convert adenine into PNA 

 guanine to greater extent than it incorporates it as adenine. Guanine has not been 

 tested in this particular yeast. In L. casei growing with adequate folic acid, the con- 

 version of guanine into polynucleotide adenine seems slightly to exceed its direct 

 incorporation.^" 



No obvious correlations seem to exist between the relative incorporations and 

 conversions of a given purine. For instance, in 0. malhaytiensis''^ guanine is incorpo- 

 rated twice as extensively as is adenine even though it is converted into PNA adenine 

 less readily than adenine is converted into PNA guanine. Diaminopurine is utilized 

 far less extensively but is transformed into adenine more extensively than is guanine. 



It would appear that not only species but also strain differences in the patterns of 

 purine utilization are possible. In a mutant of L. casei resistant to inhibition by di- 

 aminopurine, there was*' a greatly decreased ability to utilize adenine or diamino- 

 purine, accompanied b}' a reduced conversion of both. Two varieties of P. aurelia, 



" R. Abrams, Arch. Biochem. and Biophys. 37, 270 (1952). 



