JEAN BRACHET 



nucleated ones; 10 days after the operation, the non-nucleated cytoplasm contains 

 less than 30 per cent, of the initial RNA content. 



It is worth mentioning that reserve foodstuffs — glycogen and lipids — behave very 

 differently from RNA: non-nucleated halves utilize them to a small extent only 

 during the 2-3 days which follow sectioning; they then become unable to utilize 

 these reserve materials. In nucleated fragments, on the other hand, glycogen and 

 lipids undergo a much larger decrease during the early days of fasting; their utiliza- 

 tion becomes much slower afterwards, however. Total proteins also decrease faster 

 during the initial days after sectioning than afterwards : the impressive loss of RNA 

 in non-nucleated fragments thus occurs precisely when the utilization of carbo- 

 hydrates, fats and proteins has practically stopped. 



Since cytoplasmic RNA is accumulated in the microsomes, in amoebae as else- 

 where, there is no doubt that these small particles depend much more for their 

 maintenance on the presence of the nucleus than do the mitochondria. That such 

 a conclusion is of general significance is shown by the fact that, during the ripening 

 of mammalian red blood cells, the loss of the nucleus is followed by the disappearance 

 of the basophilic cytoplasmic network, which is rich in RNA. Furthermore, preliminary 

 experiments on non-nucleated Acetabularia fragments have shown that their RNA 

 content is reduced by 50 per cent, after 2 weeks (Szafarz and Brachet, 1954). 



The rapid disappearance of RNA from non-nucleated cells is obviously consistent 

 with the view, expressed by Caspersson, (1941), Marshak (1948), and Jeener and 

 Szafarz (1950), that nucleolar RNA might be a precursor of microsomal RNA. 

 However, recent experiments on Acetabularia (Brachet and Szafarz, 1953; Szafarz 

 and Brachet, 1954) in which labelled orotic acid was used as a precursor of RNA, 

 have shown that normal metabolism and turnover of the cytoplasmic nucleic acid 

 goes on for many weeks without a nucleus, at any rate in the presence of light. 



Whether the strong decrease in RNA content of enucleated amoebae is followed 

 by a reduction in protein synthesis is not yet known for certain : present work with 

 autoradiographic techniques in this laboratory indicates that incorporation of 

 labelled glycine in the proteins markedly drops when the RNA content of the non- 

 nucleated fragments decreases. There is no doubt that, in the case of the reticulocytes, 

 both the RNA content and the uptake of labelled amino-acids into the proteins go 

 down in a parallel manner (Holloway and Ripley, 1952; Gavosto, Ficq and Errera, 

 1954; Gavosto and Rechenmann, 1954). In the growing starfish oocytes, elegant 

 experiments by our co-worker A. Ficq (1953) have clearly shown that the incorpora- 

 tion of radioactive glycine into the proteins is especially active in the nucleolus and 

 in the basophilic cytoplasm, both of which are very rich in RNA. 



The problems raised by protein synthesis in non-nucleated pieces of Acetabularia 

 will be discussed more fully later on; but it should immediately be said that, here 

 again, the drop in RNA content and that in protein synthesis are parallel events. 



Enzymatic composition of nucleated and non-nucleated fragments of amoebae 



The decrease in the RNA content of non-nucleated halves of Amoeba certainly 

 means that the microsomes are seriously affected when the nucleus is removed; it is 

 unfortunately impossible as yet to say whether we are dealing with a complete des- 

 truction of some of the microsomes or with a mere alteration of their chemical 



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