125 



CARTER: Can it be by the same methods we use in the purification 

 of the virus? 



MAZIA: I think not, because the biological tests are set up so that 

 you can measure one activity if it is present in the mixture. 



CARTER: What I was thinking of was the interpretation in terms of 

 one infection per particle. 



COHN- You can say whether the characteristics you are looking for 

 in the nucleic acid are present or absent, but you cannot say that there are not 

 others present also. There could be a plurality of things in this preparation. 



SPIEGELMAN: The point is, it has been done by Stocker. It is possi- 

 ble to design the experiment so that you know whether a single event is suffi- 

 cient to get the transformation. This is the thing that you really want to know. 

 Undoubtedly it is a mixed population. 



COHN: It is not what the chemist wants to know. 



CARTER- But he has to have that information. With these molecules, 

 we must attempt to identify in some way structure with activity, and our inter- 

 pretation of structures will have to be made within that framework. Here again, 

 I think that Dr. Chargaff is going to provide us with the information we want. 



Just reviewing briefly this business of the study of the metabolism of 

 nucleic acids, in an attempt to equate activity with metabolism and in an attempt 

 to evaluate radiation effects in terms of the assimilation of isotopic precursors, 

 we can see many factors which invalidate the usual interpretations that have 

 been made and many factors which compel us to insist upon more rigorous 

 standards for future interpretations. 



I would guess that the data that Hardin Jones has on the incorporation 

 of P^2 in nucleic acid will hold. I think it is solid, and the mere fact that you 

 don't have pool sizes and a lot of things that we are beginning to insist upon 

 here, does not detract from its use. I think that perhaps the greatest use to 

 which these data have been put is in the elucidation of humoral factors working 

 at a distance from the irradiated site. Jones has used this approach to search 

 for agents which can alter the rates of incorporation of phosphorus into the de- 

 soxynucleic molecule. 



Would you like to modify that to any extent? 



JONES- I did want to bring out one point which I think gives some 

 validity to the general interpretation that is dropping back again on these bio- 

 chemical data. Everything that Dr. Kelly and I tried to do in the way of relat- 

 ing p32 turnover of the DNA fraction with mitotic counts checks if we talk about 

 times greater than 15 minutes after irradiation. There is good agreement bet- 

 ween this index of depressed DNA turnover and the other DNA \^be ling methods, 

 namely Cl4-giycine, C^^-formate, Cl4-adenine, and so on. I still think that 

 a more useful understanding of the disturbance of the mitotic process will come 

 from knowing how the separate pathways and pools of these substances can be 

 involved in depressing labeled DNA formation. 



From the Harrington data you have just shown us, it is quite obvious 

 that if the whole picture is one of consistency, there must be some metabolic 



