30 RIBONUCLEIC ACIDS AND PROTEIN SYNTHESIS 



Still greater importance is the fact that the progeny of the hybrid 

 virus contains both the RNA and the protein of the strain from 

 which the RNA originates. It is therefore the RNA which carries 

 the genetic message and which determines the specificity of the 

 protein which has been synthesized during virus multiplication. 

 Finally, Schuster and Schramm (1958) recently succeeded in ob- 

 taining mutations of tobacco mosaic virus by treating the isolated 

 RNA with nitrous acid, in order to block the amino groups of the 

 nitrogenous bases present in RNA. They found that the alteration 

 of a single base out of 3,300 nucleotides is enough to induce a mu- 

 tation of the virus. No clearer proof that RNA really is the genetic 

 determinant of the virus could be imagined. 



6. EVIDENCE FOR THE INTERVENTION OF RNA 

 IN PROTEIN SYNTHESIS IN LIVING CELLS 



We have seen that in certain microsomal systems the destruction of 

 RNA by ribonuclease treatment leads to a strong inhibition of the 

 amino acid incorporation into proteins (Allfrey et ah, 1953; Za- 

 mecnik and Keller, 1954; Webster and Johnson, 1955; Straub et ah, 

 1955). Such findings provide direct evidence of the intervention of 

 RNA in protein synthesis, especially when, as in Webster and 

 Johnson's (1955) pea root system, resumption of the incorporation 

 ability is obtained by the addition of RNA. 



Similar observations have been made by Gale and Folkes (1954, 

 1955a) (see also reviews by Gale, 1956a, b), who studied protein 

 metabolism in staphylococci which had been disrupted by ultra- 

 sonics. The permeability of the disrupted cells, which retain a large 

 proportion of their nucleic acid complement, is considerably in- 

 creased. Although they show no respiration, they are still capable 

 of amino acid incorporation into proteins, and even of net protein 

 and RNA synthesis, provided that energy sources (ATP and hexose 

 diphosphate) as well as a mixture of amino acids are present in the 

 medium. Removal of nucleic acids by various treatments, including 

 digestion with specific nucleases, greatly inhibits protein synthesis. 

 Addition of a mixture of DNA and RNA, prepared from the 



