Cytoplasmic & Nuclear Structure & Metabolism 15 



(Koritz and Chantrenne, 1954). This ability of reticulocytes 

 to synthesize proteins and to incorporate radioactive precur- 

 sors into their proteins and RNA, decreases as they lose their 

 basophilia, i.e. their RNA, in the course of the maturation 

 process. This correlation between the drop in basophilia and 

 the decrease in glycine uptake into proteins is particularly 

 obvious in autoradiographic observations by Gavosto and 

 Rechenmann (1954) : their technique allowed both processes to 

 be followed simultaneouslv. 



These results on reticulocytes are in full agreement with the 

 data from Acetabularia: removal or spontaneous elimination 

 of the nucleus does not necessarily lead to a rapid block of 

 protein synthesis. As a matter of fact, the results of the 

 experiment are chiefly dependent on the effects on cytoplasmic 

 RNA brought about by removal of the nucleus. If cytoplasmic 

 RNA is quickly broken down in the absence of the nucleus, 

 as happens in Amoeba, protein metabolism is immediately 

 affected. If, on the other hand, the non-nucleated cytoplasm 

 keeps its normal RNA content for a long time (as in Aceta- 

 bularia and reticulocytes), it can still synthesize proteins, at 

 least for a while. 



Similar instances could no doubt be found in the case 

 of eggs deprived of their nucleus: unfortunately the data 

 gathered in this field so far [by Malkin (1954) on sea urchin 

 eggs and by Tiedemann and Tiedemann (1954) on Triton 

 eggs], lack a sufficiently complete analysis. We can at least 

 state, for both the sea urchin and the newt, that the non- 

 nucleated half is no less potent than the nucleated fragment 

 with respect to incorporating radioactive precursors into 

 proteins and RNA. It is a fact, however, that in unfertilized 

 eggs, as used in the above experiments, the net synthesis of 

 proteins and RNA is likely to be negligible. It follows that 

 those results of Malkin (1954) and Tiedemann and Tiedemann 

 (1954) should probably be taken as meaning that the turnover 

 of RNA and proteins remains at its normal level in non- 

 nucleated egg cytoplasm. 



From the data available so far, we can now draw a general 



