RIBONUCLEIC ACIDS AND PROTEIN SYNTHESIS 7 



3. QUANTITATIVE CONFIRMATIONS 



A large number of independent investigations show clearly that 

 there is a good correlation between the basophilia or ultraviolet 

 absorption of different tissues and their RNA content. This paral- 

 lelism has already been pointed out by Brachet, who, in 1941, 

 estimated the RNA content of various tissues. Later, better methods 

 were devised for the determination of RNA, but the initial con- 

 clusions were not altered. Extensive reviews of the whole question 

 have been given by Davidson (1947, 1953), who made important 

 personal contributions to the subject and who came to the conclu- 

 sion that the nucleic acid content of different tissues, as determined 

 by chemical methods, is generally in accordance with the values 

 which might be expected on histological grounds. 



It was thus found, as expected, that glandular organs, which 

 synthesize large amounts of proteins (pancreas, salivary glands, 

 gastric and intestinal mucosae) are rich in RNA. The same is true 

 to a somewhat smaller degree of organs where mitoses are frequent 

 (spleen, thymus, lymph nodes, testis, various tumors) ; kidney, brain, 

 heart and lung have a much lower RNA content (see the review of 

 Leslie, 1955, for further information). 



We have seen that there is strong cytochemical evidence for the 

 view that the RNA content of cells may vary with changes in 

 physiological conditions, and that these variations are apparently 

 linked to modifications in the rate of protein synthesis. Many 

 quantitative measurements support this view. In liver, for instance, 

 fasting or administration of a protein-poor diet is followed by a 

 decrease in basophilia and a parallel drop in the RNA content 

 (Brachet et al, 1946, Davidson, 1947; Mandel et al., 1950; Camp- 

 bell and Kosterlitz, 1952; Mirsky et al, 1954; Laird et al, 1955; 

 Stenram, 1954; and others). 



The existence of a close quantitative relationship between RNA 

 content and protein synthesis is particularly impressive in growing 

 cultures of micro-organisms. Bacteria, which undergo a very rapid 

 synthesis of their own proteins during growth, are extremely rich 



References p. 50/54 



