22 Discussion 



Davidson: Are you keeping in mind that Bounce (1955, In The Nucleic 

 Acids, ed. E. Chargaff and J. N. Davidson, Vol. II, p. 147) found that 

 in isolated rat liver the nucleic acid was mainly DNA, not RNA? So 

 where can the nuclear RNA be in the rat but in the nucleolus, unless it 

 be in the chromatin? 



Bracket: I wonder how much of Bounce's material consisted of 

 nucleoli. 



Butler: If you isolate the chromatin threads it is quite difficult in 

 group preparations to detect any RNA. I don't happen to remember 

 the figure of Mirsky. 



Bracket: It came to about 10 per cent of the BNA content. 



Butler: I should say we do not find that in our analyses of thymus 

 BNA. 



Bracket: Thymus w^ould be rather different from liver, because 

 thymus nuclei stain almost completely green with methyl green- 

 pyronin. 



Butler: BNA from normal rat livers is also effectively free from 



RNA. 



Holmes: Br. Jacobson (Jacobson, W., and Webb, M. (1952), Exp. Cell 

 Res., 3, 153) showed by staining methods that, as prophase begins, 

 ribonucleoprotein is added to the outside of the chromosome. This 

 remains during metaphase and anaphase, but in late anaphase ribonucleo- 

 protein appears to be shed from the chromosomes into the cytoplasm 

 between the two groups of chromosomes. By late telophase this ribonu- 

 cleoprotein has disappeared from the nucleus. The amount found must 

 depend a little on whether the tissue is a dividing or a resting tissue, 

 and on the state of the nuclei. 



Bracket: I have had an experience similar to that of Br. Jacobson. 

 There certainly are changes in the staining ability of the chromosomes 

 during the mitotic cycle, but it is very difficult to know exactly what is 

 happening unless one makes quantitative estimations. The shape of 

 the chromosomes changes so much that it becomes extremely difficult 

 to decide whether or not there is an increase of a substance. This 

 dilution effect is dangerous in cytochemical work. 



Popjak: Since BPN synthesis is confined to the nucleus, it is not 

 surprising that the enucleated part of the amoeba eventually runs down, 

 because one of the primary acceptors of electrons from the various sub- 

 strates is gradually eliminated, and that is why vital functions cannot 

 proceed. In that connection, therefore, I wonder to what extent we can 

 ascribe a function to nuclear BNA or nuclear RNA on the one hand 

 and to the running down of BPN on the other, in the changes of meta- 

 bolism of cytoplasm. 



With regard to the experiments on the transfer of labelled nuclei, 

 where the labelling was with ^^p, is there any other evidence that the 

 label that subsequently appears in the cytoplasm is in fact associated 

 with RNA? 



Bracket: With regard to the second point, it was done by an auto- 

 radiograph method. With such a method, it is likely that many soluble 

 phosphorus-containing substances are lost. Since, after using fixative, 



