EFFECTS OF 8-AZAGUANINE ON THE SPECIFICITY OF PROTEIN SYNTHESIS 285 



of protein with which they could combine. But this certainly does not 

 completely explain what happens. When guanosine is added to intoxicated 

 bacteria, a reorganization of RNA takes place : both non-sedimentable and 

 ribosomal RNA lose the largest part of the azaguanine that they had in- 

 corporated, whereas all the pyrimidine residues that had been taken up 

 during azaguanine action are retained as polynucleotides; part of the 

 pyrimidines which were incorporated into soluble RNA are now found in 

 the ribosomal sediment. It would seem that the presence of azaguanine 

 in the ribonucleic acids prevents some normal interaction between soluble 

 and ribosomal RNA which is important for protein synthesis. 



In a discussion on the structure and function of transfer RNA [17] it 

 was pointed out that the individual transfer ribonucleic acids must be 

 recognized by the activation enzymes, and that in turn the transfer RNA 

 must recognize the different sites on the template. In this perspective, it 

 seems that transfer RNA's which have incorporated a considerable amount 

 of azaguanine are still recognized by the activation enzymes ; on the other 

 hand, it is possible that they cannot recognize the template any more. 



The differential effects of azaguanine on the synthesis of individual 

 enzymes indicates an action of the analogue on RNA fractions which carry 

 genetic information (messenger RNA or template RNA). To account for 

 the differential susceptibility of various enzymes, one can imagine that 

 certain templates are blocked, whereas others are not. This would result 

 in the production of an abnormal assortment of proteins. It is also con- 

 ceivable that the templates are all modified and that they produce abnormal 

 proteins, the abnormalities being of such a nature that certain enzymes are 

 more adversely affected than others. Incorporation of 2-thiouracil or of 5- 

 fluorouracil into RNA of Escherichia coli indeed causes the production of 

 proteins which differ from the normal ones in their serological properties, 

 enzymic activity and amino acid composition [18, 19, 20]. 



These possibilities are presently being investigated in our laboratory 

 in the case of catalase and penicillinase synthesis in B. cereus ; the work is 

 not advanced enough for results to be reported at present. A few data on 

 catalase may be quoted. The catalase which forms during restoration of 

 protein synthesis at a time when the production of active penicillinase is 

 not yet restored (see Fig. 2) was compared to the enzyme of normal 

 bacteria. No difference in sensitivity to azide or hydroxylamine inhibition 

 was detected; the concentration of inhibitor required for 50% inhibition 

 was the same for both the normal enzyme and the enzyme made during 

 restoration by guanosine. However, the relative activities of the two samples 

 of enzyme at different temperatures were markedly different, as shown in 

 Fig. 3. These activities were measured on crude bacterial extracts prepared 

 by sonication, and indirect effects cannot be completely excluded at present. 

 As the protein content of the extracts differed, an excess of serum albumin 



