PHOSPHATE METABOLISM IN THE NITCLETTS 199 



As I mentioned earlier these experiments have been undertaken to 

 provide more basic information about the metabolism of the nucleus 

 and we have not yet investigated the consequences of exposure to 

 ionizing radiation. 



ACKNOWLEDGMENT 



I am grateful to the Wellcome Trust for a Research Travel Grant wliich made 

 my participation in this conference possible. 



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DISCUSSION 



kuzin: You have said that very soon, as early as 10 min following radiation 

 exposure, changes in the DNA are observed when it is studied by chromato- 

 graphic methods using ECTEOLA cellulose. Are you sure that the DNA was 

 pure? According to the data you have presented, the nitrogen/phosphorus ratio 

 in your DNA preparation is so high that considerable protein contamination may 

 be suspected, and hence, contamination by DNAases. 



Is it not possible that this contamination accounts for the rapid depolymeriza- 

 tion you have observed? 



stocken: It is difficult indeed to determine the purity of the DNA preparations. 

 We tested for protein by the Foliu-Ciocalten test and obtained a negative result 

 which indicates less than 0-5 per cent contamination. It should also be noticed 

 that both samples were prepared simultaneously and by the same procedure. At 

 the same time we cannot say that the DNA preparations used were quite pure and 

 contained no admixtures whatsoever. 



