PHOSPHATE METAHOLISM IN THE NUCLEUS 197 



results with bacterial DNA after exposure to ultraviolet irradiation and 

 shown that the newly synthesized DNA is not the same as that in the 



conti'ols. 



The consequences of severe doses of radiation are of biochemical 

 interest but it seems unlikely that we shall in the near future be able 



Table I. The effect of 400 r X-rays total body irradiation on the 

 thymine catabolizing enzymes in regenerating rat liver 



Hours post-partial Control Irradiated 



hepatectomy 



Non operated 2-5 (4) — 



18 2-4 (4) — 



24 0-8 (4) 2-2 (8) 



36 0-6 (2) — 



48 O-^a (2) 1-65 (8) 



/[iinols catabolized/mg DNAP/30 luin. 



to reverse the effects of supra-lethal doses except by modifications of 

 replacement therapy. On the other hand if we knew exactly what was 

 the biochemical lesion caused by the near-lethal doses we might be 

 able to promote recovery without the implantation of extraneous cells. 



Our present opinion is that low doses produce a local disorganization 

 of the nucleus which alters the binding sites. Some sup]iort for this idea 

 is given by Hagen's (1960) recent work on the extractability of DNA 

 from thymus gland homogenate post radiation, and by Creasey (1960) 

 who found a leakage of Na+ and K+ from nuclei of rat thymus and 

 spleen at one hour after 1,000 r given i7i vivo. Smaller doses were 

 effective when the nuclei were irradiated in vitro. 



It is this question of what maintains the nucleus in an organized 

 state which has caused us to concentrate on some of the basic properties 

 of the nucleus. 



Allfrey et al. (1957a) have extensively studied protein synthesis in 

 isolated nuclei and shown that Na+ is an essential cation. They have 

 also discovered nuclear phosphorylation (1957b) and it may be con- 

 jectured that this might be the energy source for intra-nuclear synthesis. 



We have been concerned with another aspect of phosphorus meta- 

 bolism in thymus nuclei. When nuclei are prepared in either ionic or 

 sucrose medium both inorganic and organo-phosphate is bound to the 

 nucleus. These phosphates are only released by acid conditions or by 

 such severe mechanical damage that the nuclear structure is no longer 

 maintained. 



If a rat is killed and the thymus removed within a few seconds the 

 isolated nuclei contain phosphate predominantly as ATP. If the thymus 



