NUCLEAR SYNTHESIS OF RNA 535 



Prescott : True. But we can say that this incorporated radioactivity is RNA-ase 

 sensitive, i.e. that it is 96-98 "0 removable with RNA-ase treatment. 



Chargaff : In other words it could not have gone through a cyclic process by 

 which deamination could give a uridine derivative which was then methylated and 

 so on. 



Prescott : And got into DNA ? 



Chargaff: Yes, there are some indications that ribosides can go into deoxy- 

 ribosides; we heard about that from Dr. Reichard the other day. 



Prescott : We checked this point and found an appreciable amount of cytidine 

 going over into DNA. We next added unlabelled deoxycytidine to the medium, 

 and empirically it proved to be a good preventative for cytidine getting over 

 into DNA. 



Siekevitz : When you did the washing experiment and the activity of the RNA 

 in the nucleus went up, you made the assumption that you were not washing out 

 the precursor pool of radioactivity. You could make the same assumption about 

 the cytoplasmic RNA, that the washing experiment was not washing out any 

 radioactivity from the pool there. This would go against the idea of nuclear RNA 

 coming out into the cytoplasm. 



Prescott : Except that there is such a long lag between the presentation of 

 radioactive cytidine to the cell and the appearance of labelled RNA in the cvto- 

 plasm. You are quite right about this in one respect, however. One possible inter- 

 pretation is that the cytoplasm doesn't have the necessary kinases but the nucleus 

 does and that cytidine passes through the cytoplasm into the nucleus where it is 

 transformed into CTP. This in turn might leak into the cytoplasm where it would 

 be used for cytoplasmic RNA synthesis. I personally don't believe that this 

 happens, but it is one reason why we are looking into the pool question, particu- 

 larly whether the cytoplasm has the capacity to convert cytidine into CTP. 



Herbert: I was wondering about the resolution of your method. Is there not 

 the possibility that there is a sizeable pool of soluble RNA in the cell into which 

 radioactivity is going which you can't resolve by your technique ? 



Prescott: We are a little uncertain about the fate of soluble, or transfer, RNA 

 in these experiments. We have had some help from Dr. Waldo Cohn and hope to 

 settle the ([uestion. There could be terminal labelling in transfer RNA, and then 

 loss of the label during the acid-extraction prior to autoradiography. Approxi- 

 mately 5"o of the RNA in this cell is probably of the soluble type. We really don't 

 know for sure what is happening to that RNA. We hope to decide whether soluble 

 RNA stays in the cell with our treatment by labelling it with tritiated pseudo- 

 uridine. In this connection we are also interested in the question of where the 

 soluble RNA is synthesized ; in the nucleus, cytoplasm or both places ? 



Herbert : If it were floating free or soluble in the cytoplasni and not concen- 

 trated as it is in particles in the nucleus, then it would be very difficult to settle 

 this. Is that not true ? 



Prescott: We would pick it up. These cells are fixed in a manner which we 

 believe precipitates the soluble RNA, but we are not sure that we are not losing 

 some. 



Allfrev : I would like to raise a point that one must make the distinction 

 between end-group labelling of RNA and net synthesis of RNA as I am sure 



