276 NUCLEIC ACIDS AND GROWTH 3 



(1955), cells of £. coli adapted to gluconate contain substances which accelerate 

 the synthesis of the enzyme gluconokinase. These substances are a mixture of 

 ribosepolynucleotides. Chantrenne's (1955) experiments are of an even more 

 direct nature: when non-respiring yeast cells are synthesizing catalase under the 

 inducing action of oxygen, new RNA molecules are built up. Under Chantrenne's 

 (1955) experimental conditions, adenine is being incorporated in RNA at a faster 

 rate than in non-adapting cells and this incorporation occurs preferentially in one 

 particular cell fraction. 



Present evidence, in the case of microorganisms, is thus very strongly in favour 

 of the idea that the synthesis of a specific enzyme protein is associated with the synthesis of a 

 new, presumably specific, RNA. 



It is unfortunately impossible to say whether this statement is also valid for 

 protein synthesis in animal cells. However, cytochemical (Brachet, 1952b; Thorell, 

 1947) and biochemical (Davidson, Leslie and Waymouth, 1949) evidence suggests 

 that a high RNA content always precedes protein synthesis. More conclusive is 

 Hammarsten's (1951) opinion, drawn from his work on the incorporation of 

 labelled precursors into RNA and proteins, that nucleoprotein synthesis not only 

 precedes protein synthesis, but is even necessary for the latter to occur. This con- 

 clusion is entirely confirmed by recent work done in the author's laboratory: 

 comparative studies on the incorporation of adenine into RNA and of phenylala- 

 nine into proteins with an autoradiography method has shown that, in starfish 

 oocytes as well as in mouse liver, the incorporation of adenine is always much faster 

 than that of phenylalanine (Ficq, 1955; Ficq and Errera, 1955a; Moyson, 1955). 



[b) The role of RNA in plant-virus multiplication 



Plant viruses are extremely important in a discussion of the role of RNA in 

 growth and protein synthesis, because of their chemical simplicity : all the plant 

 viruses which have been purified and often obtained in crystalline form contain 

 only RNA (6% to 35%) and proteins. Nevertheless, these simple nucleoproteins 

 are able to reproduce themselves and are thus endowed with genetic continuity: 

 they represent therefore an ideal material for the study of protein synthesis and the 

 genetic function of RNA. In this respect, they should be compared with the DNA 

 containing T phages of E. coli, which have been discussed earlier in this chapter. 



Regarding the role of RNA in plant virus multiplication, Markham and 

 Smith's (1949) important experiments have shown that leaves infected with turnip 

 yellow mosaic virus contain two main components: the virus, and a protein 

 serologically identical to the virus, but devoid of RNA and of infectivity. The 

 fact that only the complete, RNA containing, virus is capable of multiplication 

 has led Markham (1953) to the conclusion that RNA apparently is the substance 

 controlling virus multiplication. 



These findings were soon extended to the well known tobacco mosaic virus by 

 Jeener and Lemoine (1952), Jeener, Lemoine and Lavand'homme (1954), Taka- 

 hashi and Ishii (1952) and Commoner et al. (1953): they isolated from the in- 

 fected leaves a crystallizable protein, free of RNA, immunologically identical 

 with the virus, but non-infective (soluble antigen of Jeener). 



Confirmatory evidence of the essential role of RNA in tobacco mosaic virus 



