DIFFERENTIAL DISTRIBUTION ANALYSIS 



145 



and I shall here consider the situation as it appears in the light 

 of our most recent evidence^^. When the results of the total 

 analysis of six nucleic acid specimens from two mutant strains 

 are compared (Table 32), it will indeed be seen that 5-bromo- 

 uracil and thymine are pleromeric with respect to the equality of 

 the molar quantities of purines and pyrimidines, of 6-amino and 

 6-keto nucleotides, and of 6-aminopurine (adenine) and 6-keto- 

 pyrimidines (thymine + 5-bromouracil). 



The improved methods for the determination of the distribution 

 of pyrimidine clusters^^ were applied to Preparations 1-4 (Table 

 32). The elution diagram showing the separation of the pyri- 

 midine clusters released from Preparations 3 and 4 is shown in 

 Fig. 13, the phosphorus distribution in all four preparations of 

 nucleic acid in Table 33. It may be seen (Fig. 13) that the nucleic 



TABLE 33 



DISTRIBUTION OF PYRIMIDINE NUCLEOTIDE CLUSTERS IN DEOXYRIBONUCLEIC 



ACID OF TWO THYMINE AUXOTROPHS OF E. CoU GROWN IN THE ABSENCE AND 



PRESENCE OF S-BROMOURACIL^O 



