THE PROBLEM OF NUCLEOTIDE SEQUENCE IN DEOXYRIBONUCLEIC ACIDS 8 1 



the presence of thymine, and compared it with that formed by the same 

 organism when suppHed also with 5-bromouracil [42]. This halogenated 

 pyrimidine is known to be incorporated in what would seem to be the place 

 of some of the thymine of the nucleic acid [43-45]- The results of our 

 study were, however, quite surprising. When the results of the total 

 analysis of these two nucleic acid specimens are compared (Table V), it 



TABLE V 



Composition of Deoxyribonucleic Acid of E. coli 

 Grown in the Absence and Presence of 5-Bromour.^cil* 



Growth Moles constituent per 100 moles total 

 supplements 



0-99 0-98 



T + B 0-98 1-03 1-54 



* Based on previously published results [42]. The thymine auxotroph was 

 gro\\*n on a synthetic medium (18 hr., 37 ) supplemented, per ml., with 2 ng. 

 of thymine or with 2 /ng. of thymine and 10 /tg. of 5-bromouracil. Abbreviations: 

 A, adenine; G, guanine; C, cytosine; T, thymine; B, 5-bromouracil; Pu, 

 purines; Py, pyrimidines; 6-Am, 6-amino constituents (A, C); 6-K, 6-keto 

 constituents (G, T, B). 



will indeed be seen that 5-bromouracil 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-ketopyrimidines (thymine + 5-bromouracil). It could have been con- 

 cluded that more than one-third of the places originally occupied by thy- 

 mine in the polynucleotide now were filled by 5-bromouracil. The finer 

 structural details revealed by the differential distribution analysis showed 

 this, however, not to be the case (Table VI). There took place, obviously 

 under the influence of the halopyrimidine, a severe distortion of all 

 features of the nucleotide alignment that were accessible to investigation 

 by our method. I shall return to this problem at the end of this article. 



