INTERVENTION OF RNA IN LIVING CELLS 39 



while the DNA-containing chromatin stains normally. Quantitative 

 estimations of the RNA content confirm that a marked drop 

 (20-45%) occurs. Simultaneously, the content of acid-soluble 

 nucleotides increases. The RNA content of the amoebae which 

 have been treated successively with ribonuclease and RNA is essen- 

 tially normal. RNA alone produces a small but significant increase 

 in the RNA content of normal untreated amoebae. As in the onion 

 root-tips, the oxygen consumption of the ribonuclease-treated 

 amoebae undergoes little change, while their ATP content increases 

 somewhat (Skreb-Guilcher, 1955). 



It is thus possible to modify almost at will the RNA content of 

 the amoebae by suitable treatment with ribonuclease and RNA. 

 What are the consequences of such changes on amino acid incor- 

 poration into proteins? Autoradiography experiments with i*C- 

 phenylalanine show that ribonuclease produces an almost com- 

 plete (90%) inhibition of the incorporation into the proteins. When 

 the ribonuclease-treated amoebae are placed in the normal medium 

 enriched in RNA, basophilia, as we have seen, returns to normal 

 in some of the amoebae. The autoradiography observations show 

 that a limited number of these basophilic amoebae recover the 

 capacity to incorporate phenylalanine into the proteins. (Figs. 15, 

 16, 17). Replacement of the specific RNA of the amoebae by 

 unspecific yeast RNA, although it has favorable effects on the 

 survival, the basophilia, and the motility of the ribonuclease- 

 treated organisms, does not ensure normal protein anabolism. 



In order to reach a better understanding of the mechanisms of 

 action of ribonuclease and RNA in living amoebae, more should 

 be known about the penetration of these substances in these organ- 

 isms. Our latest observations (Brachet, 1956b, Bmchet et al., 1957; 

 Schumaker, 1958) lead to the conclusion that the penetration of 

 ribonuclease into the amoebae is a very rapid process, probably 

 linked to pinocytosis. In fact, pinocytosis has been found to occur 

 even for low concentrations of ribonuclease by Chapman- Andresen 

 and Prescott (1956). Even 5 to 15 minutes after ribonuclease has 

 been added to the amoebae, their basophilia decreases, especially 

 in the nucleoli and a measurable drop (10%) in the RNA content is 

 References p. 50/54 



