Cytoplasmic & Nuclear Structure & Metabolism 13 



Even more striking is the fact that non-nucleated cyto- 

 plasm can actually effect a net synthesis of proteins and RNA. 

 Indeed, during the first days after halving, this simultaneous 

 synthesis of RNA and proteins is even more rapid in the non- 

 nucleated than in the nucleated half. Perhaps this is due to 

 the fact that the nucleus competes with the cytoplasm for 

 ribonucleoprotein precursors. If the nucleus utilizes these 

 precursors at a higher rate than does the cytoplasm (we shall 

 later see that it could very well be so), the acceleration of net 

 RNA and protein synthesis with removal of the nucleus is 

 easy to understand. 



The fact that net protein and RNA synthesis is possible in 

 the absence of the nucleus has interesting implications: for 

 instance, it is clear that, in contradiction to one of the theories 

 we have reviewed above, cytoplasmic RNA does not neces- 

 sarily originate in the nucleus. Furthermore, if RNA is 

 organized under the influence of DNA as has been suggested 

 by Gale and Folkes (1954), it is obvious that such a mechanism 

 must be a remote one. In Acetahularia, RNA synthesis is 

 certainly possible in the absence of DNA and the experiments 

 show that simple ideas such as "DNA makes RNA, and RNA 

 makes protein" are the result of an oversimplification of the 

 facts. 



It remains, however, that this RNA and protein synthesis 

 in the absence of the nucleus does not go on indefinitely : the 

 process graduaUy slows down after 10 days or so. This shows 

 again that the nucleus does exert some control on protein 

 synthesis in the cytoplasm, but this control is remote and 

 indirect, not immediate as might have been expected. 



The chemical nature of the nuclear control exerted by the 

 nucleus on protein synthesis is still unknown. It might be 

 that, as in Goldstein and Plant's (1955) experiments with 

 amoebae, part of the cytoplasmic RNA originates from the 

 nucleus in Acetahularia also and protein synthesis might come 

 to a standstill when this RNA of nuclear origin has been 

 exhausted. It would be important to know whether the 

 RNA, which is so quickly synthesized by the non-nucleated 



