490 J. BRACKET 



covered that when the basal diet contains protein, addition of energy in 

 the form of either carbohydrate or fat results in a marked increase in the 

 PNA content of the whole liver, while, when the diet lacks protein, an in- 

 crease in energy intake causes only very small changes in the amount 

 of PNA. 



The existence of a close quantitative relationship between PNA content 

 and protein synthesis is particularly impressive in growing cultures of 

 microorganisms: bacteria, which undergo a very rapid synthesis of their 

 own proteins during growth, are extremely rich in PNA: values up to 11.5 % 

 dry weight have been reported by Vendrely.^^ 



Recent work carried out in several different laboratories shows an ex- 

 cellent correlation between the synthesis of PNA and the synthesis of pro- 

 teins, if bacterial growth is studied during the logarithmic phase: for in- 

 stance, Caldwell et al.^^ find the PNA 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 recently by Northrop,*' Wade,'" and Price:'' the latter not only 

 finds the synthesis of PNA and proteins to be parallel during the logarithmic 

 phase of growth, but he also reports that when adaptative synthesis for 

 the utilization of lactose occurs, PNA increases simultaneously with the 

 protein. 



A still more recent study by Gale and Folkes'-^ shows that Staphylococci 

 synthesize protein in the presence of glucose and amino acids; if purines 

 and pyrimidines are added to this medium, nucleic acids are also synthe- 

 sized. But it is a very interesting fact that, if the medium contains no 

 amino acids, there is no nucleic acid synthesis; furthermore, 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; if the nucleic acid 

 content falls below 4%, protein synthesis stops completely. 



Gale and Folkes'^ have further found that protein synthesis and PNA 

 synthesis can, however, be dissociated by the use of antibiotics: for instance, 

 Chloromycetin, aureomycin, and terramycin inhibit protein synthesis, but 

 increase nucleic acid synthesis. Similar results, also in bacteria, had already 



" R. Vendrely, "Un symposium sur les proteines." Masson, Paris, 1946. 



88 P. C. Caldwell, E. L. Mackor, and Sir Cyril Hinshelwood. J. Chem. Soc. 1950, 



3151. 

 8' J. H. Northrop, J. Gen. Physiol. 36, 581 (1953). 

 «» H. E. Wade, J. Gen. Microbiol. 7, 24 (1952). 

 «' W. H. Price, J. Gen. Physiol. 35, 741 (1952). 



92 E. F. Gale and J. P. Folkes, Biochem. J. 53, 483 (1953). 



93 E. F. Gale and J. P. Folkes, Biochem. J. 53, 493 (1953). 



