63 



lOOOi 



y 700- 



RRAOIATED 



CONTROL 



of cells. I think there is an increase, how- 

 ever, in the amountof cellular protoplasm 

 in this time. 



CHARGAFF: An increase? 



SHERMAN: Yes, because the irra- 

 diated cells can utilize nitrogenfrom the 

 medium . 



POTTER: Do you have the specific 

 activity of DNA"? 



SHERMAN: Not for yeastbecause 

 there is not very much DNA in that organ- 

 ism. So far, we haven't been able to puri- 

 fy the DNA that we do have. We have some 

 data for liver cells but not on yeast cells. 



•3 -> 



Figure 5. The uptake of inorganic P by 

 nondividing yeast cells (S. cerevisiae) ina 

 phosphate-glucose buffer. Irradiated 

 cells exposed to 60,000 r of 200-KVX- 

 rays. Time, minutes after irradiation. 



KAPLAN: There is evidence for an 

 increase in RNA per cell in other studies 

 that might be construed as supporting this. 

 We found some time ago that RNA phospho- 

 rus per cell in irradiated thymic tissue 

 goes up by a matter of 200 or 300 percent 

 within 4 days after irradiation. We have 

 not studied it earlier. It remains up for a 

 longtime. Recently, Gardella and Lichtler (1 9), reported that after irradiation as- 

 cites tumor cells showed an increase in relative cytoplasmic volume within some- 

 thing like 1 8 or Z4 hours. That is a decrease in the nucleocytoplasmic ratio, and as 

 these cells increased in cytoplasmic volume, there was an increase in RNA and in ni- 

 trogen content of about the same magnitude. There was no change in DNA content per 

 cell, which is in agreement with other findings. 



PATT: Klein and Forssberg (ZO) observed the same thing for ascites cells a 

 few hours after X irradiation. 



CURTIS: What is the time here, Dr. Sherman? 



SHERMAN: These are 1 -hour experiments. 



CURTIS: On the basis of this, if you had waited 1 2 or 24 hours, youmighthave 

 seen more of a change, or is this not possible from the experimental point of view? 



SHERMAN: It is quite possible from the experimental point of view, but what 

 we were hoping to do was to avoid second order effects . I couldn't predict whether 

 total nucleic acid content might still be up or even higher than it is after 1 hour. 



CURTIS: If some of your cells die as others grow, itmust introduce serious 

 connplications. 



SHERMAN: Wehaven't extended it in either direction in time. Wearenow 

 trying to get shorter times because we have just recently completed some experi- 

 ments on phosphorus uptake by nondividing cells, in which we found an increased 

 rate of uptake very soon after irradiation. (Figure 5). 



COHN: Is this P^^ uptake or total phosphorus? 



