160 A. N. BELOZERSKY AND A. S. SPIRIN 



pyrimidines from bacterial RNA. The newly described pyrimidine constit- 

 uents of RNA included thymine 120 ' 122 and 5-methylcytosine, 123 which were 

 previously known only as DNA constituents. Both these pyrimidine bases 

 were shown in the RNA of E. coli, whereas thymine was also found in the 

 RNA of other bacteria (A. aerogenes, S. aureus) and in that of yeast. How- 

 ever, thymine was not found in the RNA from animal tissues, 120122 though 

 the RNA of wheat germ contained a considerable amount of thymine. 120, 122 

 The thymine content in the RNA of microorganisms was of the order of 

 1 mole % of uracil 120122 ; that of 5-methylcytosine in the RNA of E. coli 

 is said to attain up to 1-2% of all RNA nucleotides. 123 



Besides methylated pyrimidines, methylated purine bases such as 2- 

 methyladenine, 120122 6-methylaminopurine, 120 ' 122, 124 6-dimethylaminopu- 

 rine, 120-122 as well as 1 -methylguanine, 93, 124 2 -methylamino -6 -hydroxy pu- 

 rine, 93 ' 124 and 2-dimethylamino-6-hydroxypurine 93 have been found in mi- 

 crobial RNA. The former three bases (adenine derivatives) were found, 

 along with thymine, in the RNA of E. coli (B/r and 15T~), A. aerogenes, 

 yeast, and, with the exception of dimethylaminopurine, in S. aureus as well. 

 Each of them comprises from 0.05 to 1 mole % of uracil. 120122 Two other 

 bases (guanine derivatives) were found in the RNA of yeast and make up, 

 according to the authors' data, 124 about 0.01 % of the total amount of 

 purines. 



It should be noted that the above mentioned methylated bases, thymine and the 

 methylated adenine and guanine derivatives, were obtained in the form of their ribo- 

 sides and ribonucleotides. 93 ' 122 Ribose was identified as their sugar constituent. The 

 ribosides and ribonucleotides of thymine and the methylated purines were carefully 

 characterized spectrophotometrically, chromatographically, electrophoretically, and 

 compared with synthetic products. The ribonucleotides of these bases were isolated 

 from the alkaline hydrolyzate in the form of the 2'- and 3'-nucleotides, which proves 

 their presence in the RNA chain in the form of the usual 3'- to 5'-phosphoester 

 bonds. 93 ' 122 Thus, there are no grounds, at present, to doubt that thymine and other 

 methylted bases can be normal (though minor) constituents of RNA, at any rate, of 

 the RNA of microorganisms. 



As concerns a related problem with respect to the constituents of microbial RNA, 

 namely that of the incorporation of unnatural analogs of nitrogenous bases, the main 

 interest here centers on a purine analog, 8-azaguanine. This substance, a strong 

 inhibitor of bacterial growth, was shown to be incorporated into the RNA. 107 - 109 ' 126 

 Thus, 8-azaguanylic acid 107 was isolated, for the first time, from alkaline hydrolyzates 

 of the RNA of E. coli and S. mireus, which had been treated with 8-azaguanine. This 

 nucleotide amounted to 0.5% and less of the moles of the total nucleotides. It was 

 shown later that up to 40% of guanine in B. cereus can be replaced by 8-azaguanine 



120 J. W. Littlefield and D. B. Dunn, Biochem. J. 68, Proc. viii (1958). 



121 J. W. Littlefield and D. B. Dunn, Nature 181, 254 (1958). 



122 J. W. Littlefield and D. B. Dunn, Biochem. J. 70, 642 (1958). 



123 H. Amos and M. Korn, Biochim. et Biophys. Acta 29, 144 (1958). 



124 M. Adler, B. Weissmann, and A. B. Gutman, J. Biol. Chem. 230, 717 (1958). 

 126 R. E. F. Matthews and J. D. Smith, Nature 177, 271 (1956). 



