134 THE BIOSYNTHESIS OF PROTEINS 



(1958) indeed showed that a rapid RNA turnover takes place in uracil-less 

 mutants during protein synthesis. 



The question as to whether enzyme induction requires the synthesis of 

 new specific RNA molecules is not solved. Several data which were taken 

 as circumstantial evidence for a necessary RNA synthesis now appear 

 irrelevant, and no positive evidence has been afforded so far. On the other 

 hand, the pieces of evidence against the synthesis of specific RNA are not 

 completely convincing either. The problem therefore is still open. 



A more direct approach has been the search for specific RNA in adapted 

 cells. More or less crude preparations containing RNA were extracted from 

 induced bacteria and added to suspensions of non-adapted cells. In a few 

 cases, it was reported that these extracts induced the synthesis of the 

 enzyme that was looked for, although there was no regular inducer in the 

 preparations used (Minagawa, 1955 ; Reiner and Goodman, 1955 ; Hunter 

 and Butler, 1956; Nomura and Yoshikawa, 1959). Kramer and Straub 

 (1956, 1957) reported that an extract, obtained by treating a penicillinase 

 constitutive mutant of B. cereus with m NaCl at 100° C, causes the in- 

 ducible strain to produce penicillinase, provided the recipient bacteria 

 have been pre-treated with ribonuclease. Penicillinase production lasts 

 but for 20-30 min, and it is inhibited by chloramphenicol. Ribonuclease 

 abolishes the activity of the sodium chloride extract. Further analysis of 

 this interesting phenomenon is needed in order to establish whether the 

 effect is specific and whether it corresponds to an actual synthesis of enzyme 

 (Pollock, 1959). It is difficult to evaluate the significance of these observa- 

 tions; the fact that they are difficult to duplicate and that they involved 

 crude preparations is no reason to disregard them. 



Lack of clear and positive evidence for the formation of new specific 

 RNA organizers during enzyme induction encouraged the idea that induc- 

 tion and repression of enzyme synthesis rest on the control of pre-existing 

 protein forming machines (Monod, 1958; Vogel, 1957; Magasanik et ah, 

 1959). The inducers and repressors could for instance facilitate or prevent 

 the separation of the nascent protein from the assembly template (Vogel, 

 1957, 1958; Monod, 1958), or activate it in any other way. 



More recent data on the genetic control of /S-galactosidase synthesis in 

 E. coli indicate that the inducer and repressor (or more precisely the real 

 controlling agents derived from them) might actually operate a switch of 

 some sort which blocks or releases the operation of the protein weaving 

 machine. Jacob et al. (1960) showed that the regulatory genetic determinant 

 i which controls the induced versus constitutive nature of ^-galactosidase 

 synthesis controls simultaneously the expression of several structural 

 genes which are closely linked on the genetic map. A similar situation was 

 observed in the pathways of tryptophan formation (Cohen and Jacob, 

 1959) and of histidine synthesis: histidine represses the synthesis of the 



