164 A. N. BELOZERSKY AND A. S. SPIRIN 



This certainly does not in any way rule out heterogeneity of the RNA 

 within the cell, as the differences between the cellular RNA molecules may 

 be due principally, not to the differences in composition, but to other struc- 

 tural aspects, particularly the nucleotide sequence. 



b. Nucleic Acid Composition under Different Conditions and in Different 

 Functional States 



(1) DNA. Investigations of the effect of the conditions of cultivation on 

 the nucleic acid composition of microorganisms have been carried out since 

 nucleic acid specificity was first studied. It was Smith and Wyatt 85 who 

 found that the DNA composition of E. coli was not affected by the medium. 

 This was confirmed later with the DNA of other bacteria. 130 Metabolic 

 changes in the bacterial cell do not seem to affect the DNA composition; 

 for example, no differences in the DNA composition were found in A . agile 

 under conditions of nitrogen fixation, and in the same culture, in the pres- 

 ence of ammonium nitrogen. 131 



It was recently shown that the DNA of B. cereus prior to and after the 

 irradiation of the cells with ultraviolet (from 90 to 540 seconds, 600 watts 

 per 1 cm. 2 ) had an identical composition. 137 



(2) RNA. It has also been shown with respect to RNA that, despite very 

 great variations in the RNA content, far-reaching changes in the conditions 

 of cultivation and in the composition of the culture medium do not affect 

 the specificity of nucleic acid composition. An earlier statement on the 

 variability of the yeast RNA composition depending on the nitrogen nutri- 

 tion 138 proved to be erroneous. In 1952, Thomas presented data which 

 showed that when growing yeast on diverse sources of nitrogen, such as 

 ammonium sulfate, adenine, uracil, and ammonium sulfate in the presence 

 of sodium azide, no variations in the total RNA composition were to be 

 found. 139 An identical RNA composition was found in a number of Azoto- 

 bacter vinelandii samples grown under different aeration conditions. 140 The 

 nitrogen fixing Azotobacter culture exhibited no differences in the RNA 

 composition as compared to the same culture grown on ammonium ni- 

 trogen. 131 Resting cells of E. coli, and dividing cells which were shown to 

 contain 2.5 times more RNA, do not differ in their RNA composition 66 



Pardee and Prestidge have shown on E. coli cultures that the RNA com- 

 position was the same in the cells (a) under normal growth conditions, (b) 

 under conditions of an intensive protein and RNA synthesis, and (c) in 

 the presence of chloramphenicol, i.e., under conditions of RNA synthesis 



137 J. H. Stuy, J. Bacterial. 76, 668 (1958). 



13 » K. Dimroth and L. Jaenicke, Z. Nahirforsch. 5b, 185 (1950). 



139 R. Thomas, Biochim. et Biophys. Acta 8, 71 (1952). 



140 A. Lombard and E. Chargaff, Biochim. et Biophys. Acta 20, 585 (1956). 



