65 



after irradiation, before they were put back into the nutrient medium and after 

 they had been in it for an hour. 



MAZIA: It may be a little misleading to focus our attention on the 

 phosphate, since in yeast, phosphate is apparently carried into the cell in as- 

 sociation with sugar, or serves as a carrier for the sugar, depending on the 

 way we look at it. There is no evidence of straightforward diffusion of phos- 

 phate ions into the yeast cell. 



CHARGAFF: I realize that, but still it is possible during irradiation 

 of the cell. 



SHERMAN: If this happens, the transport mechanism has been re- 

 stored during the 3-hour incubation period because afterward, the specific ac- 

 tivity of these cells remained constant for as long as 20 to 24 hours. 



CHARGAFF: The experiment I have in mind would be to take yeast 

 cells grown in P-^^ to begin with; to irradiate them in the buffer, and to deter- 

 mine right after irradiation what they have lost or what the analysis is and then 

 to put them back in as you have done. 



JONES: Do the control cells have the same exposure to phosphate 

 buffer? 



SHERMAN: Yes, they do not lose phosphorus either and this has also 

 been reported by Goodman and Rothstein (21). 



DUBOIS: What was the length of the irradiation period? 



SHERMAN: These were fairly large doses. It was about 38 minutes 

 or something like that. 



CARTER: There are two things that I should like to bring up. These 

 are good data. Obviously, we all want to talk about it as much as you do. But 

 essentially we are doing a kinetic experiment from one point, which is probably 

 a fine place to start but not an adequate place to make an evaluation. 



There are several explanations for the difference in specific activity. 

 One is that your normal decay curve has simply come down below the place of 

 the decay curve in the irradiated cell. But I think that the most important prob- 

 lem we should get at is what is the immediate precursor of ribonucleic acid 

 phosphorus, because if we are told to interpret this as a new synthesis, then we 

 have to know about the comparative rates of assimilation of the immediate 

 precursor to the nucleic acid. That is why I think it is important that you do 

 rate studies at 4 or 5 different times, and these rate studies should include the 

 specific activity of the acid soluble nucleotide phosphorus; then the nucleic acid 

 specific activity should be related to these figures. If you do that, I think that 

 you are on very sound ground. At this stage of the game I think it is merely 

 conjectural. 



SHERMAN: We plan to do exactly that kind of thing. 



BENNETT: I would gather that you are inferring that the rate of syn- 

 thesis of RNA is, say, double normal from these experiments. 



SHERMAN: Approximately. 



