32. THE NUCLEIC ACIDS OF MICROORGANISMS 165 



in the absence of the protein synthesis. 141 Lombard and Chargaff confirmed 

 these observations with vast experimental material. 113 Furthermore, they 

 have shown that the addition of any of the four ribonucleosides to the me- 

 dium resulted in its intensive incorporation into the microbial RNA with- 

 out any change in its composition. 113 Also, various irradiation doses did not 

 alter the RNA composition of B. cereus. ni 



Recent work from Chargaff's laboratory 65 revealed that the RNA accu- 

 mulated in the E. coli cells in the presence of chloramphenicol (i.e., in the 

 absence of protein synthesis) was unstable and disintegrated rapidly. The 

 composition of the total RNA of the cell remained invariable both during 

 the presence of this unstable RNA and after its degradation. 65 



Thus, here we encounter the phenomenon of composition invariability 

 of RNA analogous to that observed in the studies on the influence of the 

 age of the cultures. In spite of the variability of the RNA content, the total 

 RNA composition does not change in either case. 



Thus, all the data available in the publications of recent years confirm 

 unequivocally the invariability of the DNA and RNA composition both in 

 the course of microbial growth and under different cultural conditions. 



Recently, Brawerman and Chargaff presented new data on marked differ- 

 ences in the RNA composition in green and etiolated cells of Euglena 

 gracilis 114 (see Table XI). This is a peculiar case, presumably connected 

 with the formation of specific RNA molecules in the course of the develop- 

 ment of chloroplasts. 



2. Species Specificity of Nucleic Acids 



a. DNA Composition 



The data presented by Chargaff's laboratory on the DNA of some micro- 

 organisms belonging to different systematic groups were of particular and 

 decisive importance for the discovery and the formulation of the concept of 

 the chemical specificity of nucleic acids in general. 1481 ' 142 It was shown 

 that yeast, H. influenzae, and D. pneumoniae possessed the AT-type of 

 DNA; Serratia marcescens, Bacillus schatz, and M. tuberculosis possessed 

 the DNA of the GC-type; and the DNA composition of E. coli occupied an 

 intermediate position having equimolar base proportions. 1481142 " 145 No 



141 A. B. Pardee and L. S. Prestidge, J. Bacteriol. 71, 677 (1956). 



142 E. Chargaff, Experientia 6, 201 (1950). 



143 E. Chargaff, S. Zamenhof, G. Brawerman, and L. Kerin, J. Am. Chem. Soc. 72, 

 3825 (1950). 



144 B. Gandelman, S. Zamenhof, and E. Chargaff, Biochim. et Biophys. Acta 9, 399 

 (1952). 



145 S. Zamenhof, G. Brawerman, and E. Chargaff, Biochim. et Biophys. Acta 9, 402 

 (1952). 



