ROLE OF NUCLEIC ACIDS 



77 



can even release the inhibition produced by azaguanine and completely 

 restore protein synthesis and bacterial growth if added some time after the 

 inhibition by azaguanine is established. Under those conditions, a large 

 part of the azaguanine that had been incorporated into RNA is rejected and 

 found in the medium mostly as azaguanosine (Matthews and Smith, 1956; 

 Smith and Matthews, 1957; Mandel, 1957; Mandel and Markham, 1958). 

 Restoration of protein synthesis by guanosine, however, becomes more and 



Penicillinase 



750- 



120 240 

 min 



120 240 

 min 



Fig. 22. Restoration by guanosine of the synthesis of protein material (a) 

 and of constitutive penicillinase (b), in B. cereiis after azaguanine 

 inhibition. The numbers at the end of the curves indicate the time in 

 minutes elapsed between the additions of azaguanine and of guanosine 

 (Chantrenne and Devreux, 1960). 



more sluggish when the period of azaguanine inhibition increases. An 

 unexpected feature of the recovery of protein synthesis under the action of 

 guanosine is that the synthesis of an enzyme like constitutive penicillinase 

 is not restored at the same time as net synthesis of the average protein 

 material. This is illustrated in Fig. 22. For instance, when guanosine is 

 added 45 min after the analogue, the synthesis of protein is rapidly 

 restored, whereas penicillinase formation is not yet restored 2 hrs. later (Chan- 

 trenne, 1959; Chantrenne and Devreux, 1960). There is evidence that 



