18 J. Bracket 



nucleus exerts a very real, but remote, control on the pro- 

 duction of cytoplasmic proteins. These experiments also 

 demonstrate that cytoplasmic RNA cannot originate exclu- 

 sively from nuclear RNA. 



Cases of closer control by the nucleus of protein synthesis 

 are shown by reticulocytes and especially by amoebae, in 

 which removal of the nucleus leads to a rapid decrease in the 

 incorporation of tagged amino acids into proteins and a drop 

 in RNA content of the cytoplasm. In the amoebae, removal 

 of the nucleus has different effects on various enzymes. It 

 appears that those enzymes bound to microsomes are parti- 

 cularly affected by the removal of the nucleus, while mito- 

 chondrial enzymes are especially independent of the presence 

 or absence of the nucleus. 



Finally, autoradiographic experiments have shown that, 

 in cells in which a high mitotic activity or an active protein 

 synthesis goes on, the nucleus is more active than the cyto- 

 plasm in incorporating tagged amino acids into its proteins. 



Acknowledgement 



The author wishes to thank Dr. P. Couillard, who kindly translated 

 from the French text. 



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