REGULATION 133 



Since RNA is most probably the specific constituent of the template 

 which organizes proteins, the question as to the requirement of specific 

 RNA synthesis for enzyme induction is relevant to the problem under 

 discussion. If the inducer or repressor operate at the level of the gene and 

 regulate the production of cytoplasmic replicas made of RNA, one would 

 expect enzymic induction to be accompanied by the synthesis of new 

 specific RNA molecules, the organizers of the induced enzyme. Several 

 years ago, some experimental data were quoted in favour of such a view. 

 Thus Creaser (1955) observed that the induced synthesis of a /3-galactosidase 

 in Staphylococcus aureus is stimulated by purines and pyrimidines. The 

 ability of resting yeast to form an induced a-glucosidase is strongly de- 

 pendent upon the level of the free nucleotide pool (Spiegelman et al., 1955). 

 Several purine and pyrimidine analogues were reported to inhibit the 

 induced synthesis of enzymes much more than the synthesis of constitutive 

 enzymes. However, this conclusion proved unfounded (for a discussion see 

 Chantrenne, 1958). The incorporation of labelled uracil or adenine is 

 stimulated during enzyme induction in disrupted Staphylococci (Gale and 

 Folkes, 1955) and in yeast (Chantrenne, 1956, 1958) ; this at first sight could 

 be taken as indicating the synthesis of new RNA molecules. Further 

 studies on the yeast system, however, showed that the stimulated incorpora- 

 tion was probably linked in an indirect way only to the induction process, 

 and it cannot be taken as convincing evidence for the synthesis of new RNA 

 molecules (Chantrenne, 1958; Chantrenne and Devreux, 1959). The dis- 

 covery of chain end renewal in soluble RNA (see Chapter III) adds one 

 more difficulty in evaluating the significance of increased incorporation 

 of precursors into total cellular RNA. 



Release of repression does not seem to require any RNA synthesis. The 

 formation of ornithine transcarbamylase is repressed by arginine ; it starts 

 as soon as arginine is removed from the medium. With a uracil-less strain, 

 it is possible to prevent RNA synthesis by uracil deprivation. Even so, 

 removal of arginine causes immediate synthesis of the enzyme under con- 

 ditions which prevent net RNA synthesis (Rogers and Novelh, 1959). 

 Studies on diauxie also indicated that little RNA is made during the lag 

 which corresponds to the release of repression (Magasanik et al, 1959). 

 It must be realized, however, that the synthesis of an amount of RNA 

 representing 1 per cent of total RNA would escape observation; and the 

 amount of RNA that one would expect to be synthesized during adaptation 

 would not exceed that value : there are several hundred different proteins 

 in a bacterial species, there must be as many specific RNA varieties ; the 

 appearance of one new type of template RNA among several hundred pre- 

 existing RNAs would indeed be very difficult to detect by quantitative bio- 

 chemical determinations. Moreover, the absence of net synthesis does not 

 mean that no new molecular species of RNA can form; Earner and Cohen 



