16 J. Bracket 



conclusion: the nucleus exerts, at the most, only a remote 

 and delayed control on the synthesis of cytoplasmic proteins. 

 It does not necessarily follow that the actual role of the 

 nucleus is negligible in the synthesis of proteins in the whole, 

 intact cells. We have already recalled the results from the 

 laboratories of Mirsky (Daly, Allfrey and Mirsky, 1952) and 

 of Davidson (Crosbie, Smellie and Davidson, 1953; Smellie, 

 Mclndoe and Davidson, 1953) in which it was established 

 that some nuclear proteins take up marked amino acids at a 

 rate comparable to that of the whole of cytoplasmic proteins. 

 We have pointed out on this occasion that the methods used 

 in isolating these nuclei may well involve the loss of soluble 

 proteins which might be very active metabolically. 



This criticism is motivated by some recent autoradio- 

 graphic observations. When amino acid incorporation into 

 proteins is followed by this method, a much higher activity 

 is found in the nucleus than in the cytoplasm. This has been 

 shown for various materials: growing oocytes (Ficq, 1953), 

 amphibian eggs in the course of their development (Ficq, 

 1954; Sirlin, 1955) and mammalian liver (Ficq and Errera, 

 1955; Moyson, 1955). This higher activity of the nuclei 

 becomes much less obvious when the liver sections are 

 extracted by dilute citric acid, as used for the isolation of 

 nuclei. It appears possible, therefore, that this acid extracts 

 some metabolically active proteins from the nuclei. This 

 might be shown conclusively by a study of radioactive 

 amino acid incorporation into nuclei isolated in non-aqueous 

 media. 



These autoradiographic studies have not been carried out to 

 a sufficient extent to allow general conclusions to be drawn 

 from them. It is by no means certain that the nuclei of all 

 cells are more active in this manner than the cytoplasm : that 

 has only been shown, so far, for cells with a high rate of 

 protein synthesis (oocytes, livers) and for actively dividing 

 cells (embryos in the course of development). 



The autoradiographic experiments of Ficq (1953, 1955) on 

 starfish oocytes are more informative. In this material, it 



