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Discussion 



Campbell : If I understand it right the incorporation of your azaguanine into 

 the S-RNA makes your system rather different from that of Dr. F. Gros of the 

 Institut Pasteur in which there was very little incorporation of fluorouracil into his 

 S-RNA ? 



Chantrenne: These were very short experiments, a matter of 10 or 20 sec, if 

 I remember correctly. 



Campbell: But later on the label moved to 70S and not S-RNA ? 



Chantrenne: Yes. In the case of azaguanine, there are two effects. The first is 

 an inhibition of protein synthesis ; it might be due to an action of the analogue 

 on GTP or on S-RNA which prevents this from interacting normally with the 

 ribosomes. The second effect bears on the specificity of protein synthesis, and in 

 this respect it resembles very much that observed by Gros with fluorouracil; it 

 might concern the genetic messenger or the ribosomes. 



Chargaff: Fluorouracil goes very largely into the S-RNA; it actually replaces 

 more uracil of the S-RNA than it does of the ribosomes. 



Herbert: In Dr. Gros's experiments fluorouracil inhibited DNA synthesis 

 and he had to add thymine to restore it. 



Chantrenne: Yes, that is right. 



Herbert : Does azaguanine affect DNA synthesis ? 



Chantrenne: With low concentrations of azaguanine, DNA synthesis is not 

 inhibited. To get an inhibition, you must use rather large concentrations and even 

 so the inhibition establishes only after about one or one and a half hours. The 

 incorporation of azaguanine into DNA is very low, but it might possibly be sufficient 

 to cause changes in specificity. 



