126 ROLE OF THE CELL NUCLEUS 



experimental results of Nizet and Lambert (1953) readily show that 

 an actual synthesis of hemoglobin occurs in reticulocytes. It should 

 finally be added that autoradiographic observations by Gavosto 

 and Rechenmann (1954) have shown that an excellent correlation 

 between basophilia and incorporation of glycine into the proteins 

 exists in reticulocytes : during the ripening of the erythrocytes, loss 

 of basophilia and decrease in the incorporation go hand in hand. 



Less is known about possible RNA synthesis in reticulocytes 

 although recent isotope experiments of Kruh and Borsook (1955) 

 indicate that they do incorporate radioactive glycine into their RNA. 



The results obtained on reticulocytes are thus in full agreement 

 with the data drawn from Acetabularia. The removal or sponta- 

 neous elimination of the nucleus does not necessarily lead to a rapid 

 block of the mechanisms for RNA and protein synthesis. 



Similar conclusions can be drawn from the few data that we 

 possess for amphibian and sea urchin eggs, where the analysis has 

 not as yet been pushed very far. In Triton eggs, Tiedemann and 

 Tiedemann (1954) studied the incorporation of radioactive carbon 

 dioxide into various chemical constituents, especially proteins and 

 RNA. Working with eggs separated into two by ligation, they found 

 no significant difference between the nucleate and the enucleate 

 halves. In unfertilized eggs separated into "light" and "heavy" 

 halves by Harvey's (1932) centrifugation method, Malkin (1954) 

 observed a stronger incorporation of radioactive glycine into the 

 RNA of the enucleate heavy halves than in the other. The difference 

 was not so striking when Malkin (1954) studied the incorporation 

 of the same precursor into the proteins. But the important fact re- 

 mains that Malkin found considerable incorporation to occur in 

 both the RNA and proteins of the enucleate egg fragments. It 

 should be added, however, that these experiments of Tiedemann 

 and Tiedemann (1954) and of Malkin (1954) can hardly be taken 

 to prove that RNA and protein synthesis occurred in the absence 

 of the nucleus. It is likely that net syntheses of protein and RNA 

 are negligible in unfertilized eggs and that we are dealing, in fact, 

 with a turnover. The latter obviously remains at its normal level in 

 enucleate egg cytoplasm. 



