18 RIBONUCLEIC ACIDS AND PROTEIN SYNTHESIS 



and Earner's (1954, 1955) conclusions have been confirmed by Ben- 

 Ishai and Volcani (1956), who found that in thymine-less E. coli 

 there is a constant ratio between protein synthesis and RNA syn- 

 thesis. Inhibition of RNA synthesis leads to an inhibition of protein 

 synthesis, but the reverse is not true. It is thus to be concluded that 

 protein synthesis is dependent on RNA synthesis. 



Interesting results which lead to similar conclusions have also 

 been obtained with UV-irradiated bacteria. Experiments of Kelner 

 (1953) and of Kanazir and Errera (1954) show that low doses of 

 UV radiation have little effect on RNA and protein synthesis ; while 

 they completely stop DNA synthesis, the result again being the 

 production of filamentous bacteria. Ultraviolet irradiation also 

 inhibits the induced synthesis of galactozymase in yeasts (Swenson, 

 1950; Halvorson and Jackson, 1956). The latter conclude that DNA 

 synthesis in yeasts can be inhibited by UV doses which do not stop 

 RNA and protein synthesis. The UV doses which inhibit the in- 

 duced synthesis of glucosidase also inhibit the incorporation of 

 glycine into RNA and protein. Ultraviolet light, as well as amino 

 acid analogues, are especially effective in preventing the synthesis 

 of glucosidase, when applied during the latent period which pre- 

 cedes the actual synthesis. Both apparently act on some precursor 

 system, in which RNA seems to be involved. 



Still more relevant is Price's (1952) finding that, while staphylo- 

 cocci adapt to lactose, protein synthesis never occurs without a 

 simultaneous increase in RNA. His observations strongly suggest 

 that the synthesis of a new enzyme is linked to the synthesis of new 

 RNA molecules. 



This last suggestion has recently received a good deal of attention, 

 especially in Pardee's (1954, 1955) and Spiegelman's (1955) labora- 

 tories. Pyrimidine-requiring mutants of E. coli can synthesize in- 

 duced enzymes only when the medium is supplemented with the 

 required bases. Pardee's experiments (1954, 1955) lead him to the 

 conclusion that continuous production of new RNA molecules is 

 necessary for induced enzyme synthesis, and that the bulk of 

 bacterial RNA is inert in this process. Furthermore, Pardee and 

 Prestidge (1955) found experimental conditions in which both RNA 



