32. THE NUCLEIC ACIDS OF MICROORGANISMS 177 



cept was favored, together with the analogy to the species specificity of 

 DNA, and also with the data obtained by means of the study of the RNA 

 composition of isolated RNA preparations. 



Reliable and trustworthy data with respect to the specificity of the RNA 

 composition became available only when the necessity was realized of study- 

 ing its composition directly on the biological material without the isolation 

 of the RNA in the form of purified preparations (so as to prevent secondary 

 changes in composition due to fermentative and chemical effects). The 

 work of Thomas, who studied the RNA composition of the yeasts by means 

 of direct hydrolysis of the cells, was one of the first to point to this neces- 

 sity. 139 Investigations on a wider scale were undertaken in Chargaff's lab- 

 oratory. 153155 On the basis of such investigations it became possible to 

 formulate general regularities of the native RNA composition 154, 155 ; this 

 was a very important factor in judging the reliability or unreliability of the 

 data obtained. "Chargaff's rule" (G + U = A + C) is thus, at present, 

 the main criterion of the native character of the RNA composition. 



The data on the RNA composition in bacteria and actinomycetes are 

 presented in Tables VIII and IX, those for fungi in Table X, and those for 

 algae and protozoa in Table XL 



When reviewing the analytical data in all of these tables it should be 

 noted that the regularity stated from Chargaff's laboratory 154 ' 155 — (G + 

 U = A -f- C) — was completely confirmed; at any rate, when the analysis 

 was performed directly on the material and not on isolated preparations. 



When analyzing the RNA composition of bacteria (Tables VIII and IX), 

 we are struck by the comparatively small variation range of the RNA 

 composition when passing from species to species. Thus, according to our 

 own data, 146 ' 156 the molar content in guanylic acid fluctuates in different 

 species of bacteria from 26.7 to 33.0%; that of adenylic acid from 22.6 to 

 28.1 %; cytidylic acid from 21 to 26.1 %; and that of uridylic acid from 18.3 



153 D. Elson, I. Gustafson, and E. Chargaff, /. Biol. Chem. 209, 235 (1954). 



154 D. Elson and E. Chargaff, Nature 173, 1037 (1954). 



155 I). Elson and E. Chargaff, Biochim. et Biophys. Acta 17, 367 (1955). 



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