8 RIBONUCLEIC ACIDS AND PROTEIN SYNTHESIS 



in RNA. Values up to 11.5% dry weight have been reported by 

 Vendrely (1946). 



Work carried out in several different laboratories shows the exist- 

 ence of an excellent correlation between the synthesis of RNA and 

 the synthesis of proteins, provided that the bacterial growth is studied 

 during the logarithmic phase. For instance, Caldwell et al. (1950) 

 found the RNA content of bacteria to be proportional to the growth 

 rate, whatever the experimental conditions (changes in the nitrogen 

 source of the culture medium, presence or absence of inhibitors, 

 normal organisms or slow-growing mutants). Similar findings have 

 been reported by Northrop (1953), Wade (1952) and Price (1952). 



An important study of Gale and Folkes (1953) shows that staphy- 

 lococci synthesize proteins in the presence of glucose and amino 

 acids. If purines and pyrimidines are added to this medium, nucleic 

 acids are also synthesized. But the interesting fact is that if the me- 

 dium contains no amino acids there is no nucleic acid synthesis, 

 whereas the presence of purines and pyrimidines in the medium 

 enhances protein synthesis. There thus exists a strong positive 

 correlation between the nucleic acid content of the cells and the 

 rate of protein synthesis. 



Gale and Folkes (1953) have also found that protein synthesis 

 and RNA synthesis can be dissociated by the use of antibiotics. For 

 instance, Chloromycetin, aureomycin, and terramycin all inhibit 

 protein synthesis but increase nucleic acid synthesis. However, there 

 is very good evidence (Neidhardt and Gros, 1957) for the view that 

 the RNA formed in the presence of the antibiotics is abnormal in 

 many respects ; it is therefore not surprising that it cannot support 

 protein synthesis. We have already seen that the same situation can 

 be found in the ovary and testis by autoradiography. 



The very great importance of the culture conditions in experi- 

 ments on microorganisms cannot be overemphasized. As was 

 shown very clearly by Jeener (1952, 1953), the relationship between 

 RNA content and protein synthesis is very different in the case of 

 the flagellate Polytomella coeca, whether one is dealing with a 

 continuous culture (in exponential phase of growth) or not. If cells 

 are compared during the various stages of growth of a culture, there 



Text continued on p. 17 



