Nuclear control of enzymatic activities 



J. Brachet. Our results are compatible with the view that RNA bound to the micro- 

 somes is important for protein synthesis, an opinion for which Mirsky's group has 

 recently found fresh evidence. I think that they are compatible with Professor 

 Danielli's hypothesis, without however giving it direct support. 



G. Pontecorvo. What is the evidence for active synthesis of RNA within the nucleus, 

 and for this RNA being the same as, or a precursor of, the cytoplasmic RNA ? 



J. Brachet. There is no doubt that although the decrease of RNA after removal of the 

 nucleus is consistent with the idea that nuclear RNA might be a precursor of cyto- 

 plasmic RNA, it does not prove that relationship : the facts can easily be explained 

 by other hypotheses. On the other hand it is now certain that in many types of cells 

 the incorporation of labelled precursors of RNA ( 32 P, orotic acid) occurs very much 

 faster in the nucleus than in the cytoplasm: this fact has been taken to show that 

 nuclear RNA is a possible precursor of cytoplasmic RNA. However, a recent 

 mathematical analysis of the data by Barnum and Huseby indicates that in cancer 

 cells at any rate, nuclear RNA cannot be the precursor of cytoplasmic RNA. It 

 thus seems that nuclear and cytoplasmic RNA are being synthesized independently, 

 the former at a much faster rate. 



E. W. Temm. With regard to the possibility that nucleic acids may have a stabilizing 

 action on proteins in the cell, the case of virus particles is relevant. It is well estab- 

 lished that these are often nucleoproteins and there is evidence from the use of 

 tracers that, once formed, they do not take part in replacement or exchange reactions 

 to the same extent as normal cytoplasmic proteins. The relatively large amounts of 

 nucleic acid associated with proteins in nuclear structures may be a significant factor 

 favouring stability of the proteins at certain stages of development of the cells. 



J. Brachet. Dr. Yemm's suggestion is very interesting; it is true that DNA and histone, 

 in experiments with isotopes, also show an unusual stability. However, the other 

 nuclear proteins are metabolically much more active. 



R. J. Goldacre. Have you any views on the part played by the nucleus in the loco- 

 motion of Amoeba? In contrast to the long-term and indirect effects of enucleation 

 which have just been described, the effect on the locomotion of amoebae is a rapid 

 one, and the dramatic revival of active locomotion on replacement of the nucleus 

 may take only a few minutes or even seconds. Have any chemical changes been 

 correlated with the loss of active locomotion ? 



J. Brachet. I do not know what chemical change takes place. The decrease in the 

 uptake of 32 P in non-nucleated halves of Amoeba discovered by Mazia also occurs 

 very quickly after loss of the nucleus. I might also mention that non-nucleated halves 

 stain uniformly with neutral red in vivo, whereas nucleated ones show the accumula- 

 tion of the dye at the 'tail' described by Goldacre; furthermore, when a vitally 

 stained Amoeba is cut in two, this accumulation of dye very quickly disappears from 

 a non-nucleated half. 



R. D. Keynes. Does the effect of enucleation on the uptake of 32 P follow or precede 

 the effect on the ATP content ? In other words, is the uptake reduced merely when 

 the internal ATP falls, or is there a direct connexion between enucleation and uptake 

 of phosphorus which is independent of the amount of ATP already in the cell ? 



H 103 



