IV RNA AND GROWTH PROTEIN SYNTHESIS 275 



synthesis is found only in continuous cultures, where growth maintains itself at 

 a constant rate, which can be controlled at will by the investigator. 



Later work by Gale and Folkes (1953) has also shown that, in Staphylococcus, 

 there exists a strong correlation between the nucleic acid content of the cell and the 

 rate of protein synthesis; however, antibiotics like Chloromycetin, aureomycin and 

 terramycin can dissociate the two processes : protein synthesis is inhibited, while 

 RNA synthesis is increased. 



Mention should also be made of a paper by Price (1952), who obtained similar 

 results on Staphylococcus muscae: in his experiments, the increase in proteins is accom- 

 panied by a parallel increase in RNA, in contrast to DNA. Furthermore, the 

 RNA/protein ratio is proportional to the growth rate. While the RNA content per 

 cell depends on the growth rate during early logarithmic phase, the DNA content 

 per cell remains fairly constant irrespective of the growth rate of the cells. 



An important finding of Price (1952) is that, while the cells adapt to lactose, 

 there is never an increase of protein without a simultaneous increase in RNA. This 

 observation is of interest because it raises an important question : is the synthesis 

 of a new enzyme linked to the synthesis of new RNA molecules? 



This interesting problem has been receiving more and more attention lately: 

 for instance, Pardee (1954, 1955) has found that purine- and pyrimidine-requiring 

 mutants of E. coli can synthesize adaptive enzymes only when these bases are 

 added to the medium. The synthesis of induced enzymes stops as soon as the 

 purines and pyrimidines are removed from the culture medium. The obvious 

 conclusion is that continuous production of new RNA molecules is necessary for 

 specific protein synthesis and that the bulk of bacterial RNA is metabolically inert. 



Comparable results have been described by Gale and Folkes (1955a), who 

 obtained stimulation of the induced synthesis of glucozymase on addition of a 

 mixture of purines and pyrimidines to disintegrated Staphylococci . 



But the most complete and recent analysis of the phenomenon is that of Spiegel- 

 man et al. (1955): they have found that strong interference with DNA synthesis 

 has no striking effect on enzyme formation, whereas a 50% inhibition of RNA 

 synthesis completely suppresses the enzyme-synthesizing capacity. Uracilless and 

 adenineless mutants of £. coli are unable to synthesize an adaptive enzyme, unless 

 the needed metabolite is added to the medium (in accordance with Pardee's [1954] 

 results). Addition of purine and pyrimidine analogues, which interfere with 

 nucleic-acid synthesis, immediately stop the adaptive enzyme synthesis of ^- 

 galactosidase in E. coli. 



This last result of Spiegelman et al. (1955) has been confirmed by Greaser 

 (1955a, 1955b), who obtained inhibition of induced synthesis of p-galactosidase, 

 catalase and ghicozymase in Staphylococcus, on the addition of purine analogues 

 (azaguanine and 2,6-diaminopurine) ; he also obtained some indications of a 

 synthesis of new DNA and RNA molecules during adaptive synthesis of the enzyme. 



Pardee (1954, i955)> Spiegelman et al. (1955) and Greaser (1955a, 1955b) 

 arrive at the same conclusion: synthesis of new RNA is a compulsory concomitant 

 of the continued formation of new enzyme molecules. 



Gonfirmations of this conclusion can be found in recent papers by Reiner and 

 Goodman (1955) and Ghantrenne (1956): according to Reiner and Goodman 



Literature p. sgg 



