RNA AND CONTROL OF CELLULAR PROCESSES 115 



synthesis. The experiments of Kramer and Straub (1956) showed 

 tliat the destruction of existing RNA l)y ribonuclease prior to in- 

 duction did not impair inducibihty, while ril:)onuclease applied after 

 the inducer prevented new enzyme formation. The inhibition of 

 RNA formation bv analogs" prevents induction ( Spiegelman et at., 

 1955; Creaser, 1956). If RNA formation is tlie primarv effect of 

 induction, DNA should be necessary. McFall et al. (1958) have 

 found that when bacterial DNA is destroyed by "suicide" after in- 

 corporation of P"-, the abilit\' to form induced enzymes is lost. Gale 

 and Folkes (1955) were able to induce /3-galactosidase formation 

 in homogenized preparations of E. coli. The induction was effec- 

 tively suppressed with desoxyribonuclease and reinstated by the 

 addition of bacterial DNA. It is probable then, tliat the inducer 

 does not act on the enzyme forming site, but rather activates the 

 formation of new RNA. 



If RNA s\ nthesis is necessary for the synthesis of induced pro- 

 teins, then an increase of the svnthesis of the specific RNA should 

 be the first effect of induction. It would be difficult to find such an 

 increase, since onlv a small proportion of RNA formed is used for 

 enzyme formation. However, if RNA must be formed first, a certain 

 delav between the addition of the inducer and the beginning of 

 enzyme production should be noticeable. While the synthesis of 

 a protein molecule in the cell takes a very short time ( McQuillen 

 et al, 1959; Zalokar, 1959b), it seems that the synthesis of an RNA 

 molecule is slower. Kinetic studies of the uptake of C^^ adenine 

 and C^^ uridine into Neurospora and incorporation into its RNA 

 (unpublished results) indicate that a few minutes are necessary to 

 build up an RNA molecule. A similar conclusion was reached by 

 Yeas and Vincent ( 1960 ) for the synthesis of RNA in yeast, using 

 P'^- as a precursor. If this is the case, there should be a delay of at 

 least a few minutes between induction and the onset of enzyme 

 production. In the induction of penicillase, a latent phase of about 

 10 minutes was found (Pollock, 1952). No such lag seems to be 

 observable in the induction of /3-galactosidase and some other in- 

 ducible enzymes (Pollock, 1959). A short lag, of a few minutes 

 or less, could easily be overlooked or not measurable by the methods 

 used in these studies. If the induced enzyme begins to be formed 

 immediatelv after induction and proceeds at a linear rate, it would 

 be difficult to assume prior RNA svnthesis. In such a case, an acti- 

 vation of the preexisting enzyme-forming site should be considered. 



