On the Species Specificity of the Nucleic Acids of Bacteria 329 



When we compare RNA composition in initial and experimentally produced 

 forms of bacteria (see Tables 5 and 6), we are struck, first and foremost, by the 

 fact that DNA exhibits marked qualitative differences and alterations, whereas 

 the RNA composition remains constant. The DNA composition and its changes 

 are in good correlation with the alteration in the whole sum of hereditary pro- 

 perties. Thus, the alkali-producing form standing out in its biological [12, 13], 

 chemical [14] and antigenic [13, 14] characteristics, as compared with both the 

 original culture E. coli and the 'leader' culture of Breslau bacteria stands out 

 just as prominentiy in DNA composition. The paratyphoid which arises from 

 this alkaU-producing form upon further influence and which is a culture similar 

 to Breslau bacteria [13, 14] resembles these Breslau bacteria in DNA composition. 

 In the Hght of these data it is difficult not to link up the specificity of cell DNA 

 with the entire specificity of the nature of the organism. The correlation of 

 changes in the specificity of DNA composition with changes in the antigenic 

 specificity of the investigated cultures [13, 14] leads us to think that DNA is 

 cormected with specific protein synthesis, with the biological mechanism deter- 

 mining the specificity of proteins. Curiously, it is RNA, which many investi- 

 gators now hold responsible for the specificity of protein synthesis, that does 

 not alter its composition in the event of such profound change in the specificity 

 of cell proteins. This leads us to the question of whether the entire specific role 

 in protein synthesis can be ascribed to RNA alone. Furthermore, can the view 

 that there is a direct genetic connection with the DNA in a cell be accepted 

 without reservations ? It is difficult to assume that, with the DNA composition 

 so diff"erent, it will in some measure determine the S5nithesis of so identically 

 composed RNA, just as it is difficult to assume the possibility of a direct transi- 

 tion of DNA into RNA, and vice versa. In this connection we would express 

 doubt about possible direct interconversions between these two nucleic acids 

 in processes of development, a viewpoint which became widespread after the 

 investigations of Brächet in the thirties. Indeed, it is difficult to suppose that the 

 interconversion of these nucleic acids could be effected in defiance of the disparity 

 of their nucleotide composition. 



Nevertheless, on the basis of the fact of positive correlation between the 

 composition of RNA and DNA it is not excluded that some small portion of 

 RNA (perhaps the fimctional analogue of nuclear RNA) depends upon DNA, 

 being determined by its structure, or may be directly transformed into it and 

 vice versa. But still, with respect to the main mass of RNA in the cell, we regard 

 any possibility of its direct transformations into DNA and vice versa as hardly 

 possible. 



It is more probable to assume that should these nucleic acids be interdependent 

 in the process of development, this is a mere paralleHsm of phenomena, perhaps 

 interconnected, but based on different biosynthetic pathways. 



In conclusion, a few considerations concerning the evolution of nucleic acids. 

 There is no shadow of doubt about the fact that the nucleic acids played a sig- 

 nificant part in the evolution of the organic world. However, it is doubtful that 

 both RNA and DNA appeared simultaneously at the early stages of the develop- 

 ment of life. The author of the present commvmication is inclined to think that 



