On the Species Specificity of the Nucleic Acids of Bacteria 



325 



These results are also at variance with the concept of intracellular hetero- 

 geneity of RNA, at least in regard to composition. It is well known that the 

 RNA content undergoes marked quantitative changes in the process of onto- 

 genesis. Specifically, in the case of bacteria in the stationary developmental 

 phase the amount of RNA ranges from | to ^ of the amount in the logarithmic 

 phase of growth. In our case, for example, the lo-hour Escherichia coli culture 

 contained 9-6% RNA, whereas the 30-hour culture contained only 5-3% (in 

 dry weight of bacterial mass). Total RNA composition can be constant in the 

 event of such pronounced changes of its quantitative content if all the RNA 

 molecules in the cell have roughly the same nucleotide composition, i.e., if 

 there is no intracellular heterogeneity of the RNA molecules with regard to 

 their composition. Another assumption is that the cell contains a number of 

 RNA fractions of different composition, but in the age and associated metabolic 

 changes there takes place an identical, vmiform decrease or increase of the 

 mmiber of RNA molecules in each of these fractions. This supposition appears 

 less probable, because functionally different fractions should behave differently. 



In Table 3 we see the comparative data for DNA composition, and in Table 4, 

 for RNA composition, in bacteria belonging to different systematic groups. 



Table 3 

 DNA composition of different bacteria 



