EFFECTS OF 8-AZAGUANINE ON THE SPECIFICITY OF PROTEIN SYNTHESIS 283 



instance, the synthesis of catalase is restored almost at the same time as 

 the average protein material ; for some time during restoration the rate of 

 catalase formation per weight of newly formed protein material is even 

 greater than in normal bacteria (Fig. 2). 



Clearly, besides inhibiting protein synthesis in general, the purine 

 analogue must jam some mechanism upon which the specificity of protein 

 synthesis depends. 



Cells or bacteria which are unable to incorporate azaguanine into 

 ribonucleic acids and nucleotidic compounds are insensitive to the analogue 



750 

 ^1 500 



c 



V 



i 250 



■1,500' 



V 1.000 



500 



Fig. 2. Restoration of the synthesis of protein material, catalase and penicil- 

 linase [7]. Two growing suspensions of B. cereiis (penicillinase-constitutive mutant) 

 in a casein hydrolysate were shaken in a water bath at 30 . At time o, each sus- 

 pension received o*o8 ^tC L-[^^C]-phenylalanine and 36 ^ig. 8-azaguanine per ml. 

 Guanosine (135 /^tg./ml.) was added respectively at the same time as 8-azaguanine 

 (control, clear points) and 45 min. later (black points). 



O, • : ^■'C in protein materia! per ml. suspension. 



A, A : Penicillinase activity (units per ml. suspension). 



V, ▼ : catalase activity, per ml. suspension. 



[8, 9]. The inhibitory action of azaguanine therefore is probably due to 

 some harmful synthesis of nucleotidic compounds containing the analogue 

 instead of guanine. Since guanosine triphosphate is required for the passage 

 of the amino acids from transfer RNA to the nascent polypeptides on the 

 ribosomes [10, 11, 12, 13], an obvious possibility is that azaguanosine 

 triphosphate might interfere at this stage. The degree of inhibition of 

 growth is indeed more closely correlated with the concentration of azagua- 

 nine in acid soluble compounds than with the total amount of analogue in 

 the nucleic acids [i]. On the other hand, in Tetrahymena geleii which 

 requires exogenous uracil to make RNA, the degree of inhibition of 

 growth by azaguanine depends on the level of uracil in the medium [14] 



