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ent kinds of molecules, in all probability, and we probably have to have about as 

 many different kinds of RNA as there are biological functions for RNA to serve 

 in the cell. The same goes for DNA. It may be convenient shorthand but it is 

 very misleading shorthand to talk about one kind of DNA or RNA. 



BENNETT: Isn't it also true in irradiation effects, that the number of 

 reactions one can expect to take place are considerably less than the total num- 

 ber of molecules by many factors of 10. This effect cannot be occurring in 

 every DNA molecule; it would have to be on a very small number of the DNA or 

 RNA molecules. 



POLLARD: If you assume that irradiation acts only on RNA in yeast 

 and that it is a definite factor of 1 , i.e., that you get 1 molecule inactivated in 

 order to take 10 mg. of RNA per cc. of yeast cells down to 9 mg. , then the RNA 

 will have to have a molecular weight of about 5x10. 



CHARGAFF: Would that also hold if the RNA were together with a hunk 

 of protein? 



POLLARD: This means no recombination of the radical. No effect on 

 the protein at all. 



TOBIAS: What is the radiation dose? 



POLLARD: 100 r. 



TOBIAS: That is a pretty low dose for yeast. We would give maybe 



600 r. 



POLLARD: On the other hand, yeast is rather dry. 



TOBIAS: No, yeast contains a reasonably high percentage of water. 

 My calculations are done in a somewhat different way. We know that there is 

 about 10 times as much RNA in a yeast cell as DNA. Further, we may take the 

 molecular weight of each RNA and DNA as 10 ', and endow RNA particles with ap- 

 proximately the same radiosensitivity as DNA particles. From elementary prob- 

 ability considerations it follows that the number of cells in which at least 1 RNA 

 molecule out of 10 would be inactivated is about 10 times greater than the number 

 of cells in which a DNA molecule is inactivated. 



POLLARD: I wonder if you should not look for some sort of propaga- 

 tion. Wouldn't it be more reasonable to say that there is a sort of biological 

 multiplication that increases the number of inactivated molecules? Every time 

 I have made this calculation I have stopped; it seems to be unreasonable. It 

 seems to me more reasonable to suppose that you are hitting one molecule which 

 divides many times and it is that process that has to come to a stop. 



SHERMAN: With just one wrong molecule do you not have to postulate 

 that this is being propagated selectively? It is in competition with a lot of other 

 fairly normal molecules. 



POLLARD: I suppose that competition ultimately wins so that the cell 

 goes on its way and survives, but in the case where it does not survive, what 

 happens? There must be some selective mechanism. 



SHERMAN: I am not trying to say that I know what happens. I just say 

 that this is a rather disturbing number, although it does not seem to bother Dr. 



