ON THE ROLE OF THE CELL NUCLEUS 



AND ITS FRACTIONS IN PROTEIN BIOSYNTHESIS 



AS EVIDENCED FROM INCORPORATION 



OF LABELED AMINO ACIDS 



« 



I. B. ZBARSKY and K. A. PEREVOSCHIKOVA 



Biochemical Laboratory, State Oncological Institute 

 Moscow, USSR 



Lebelled eimino acids (glycine-C", lysine-C", methione-S") injected into 

 rats or mice, incorporate into nuclear proteins of liver spleen and other 

 normal tissue cells only slightly less intensively than into the whole 

 tissue proteins. The highest rate of radioactivity incorporation among 

 nuclear proteins was found to be in the "acid protein" fraction which 

 represents the ribonucleoproteins of nucleoli. The deoxyribonucleoprotein 

 fraction is less active, while the residual protein forming nuclear membrane 

 shows the least activity. 



Tumor cell nuclei show much lower incorporation and differ from normal 

 cell nuclei in distribution of radioactivity among nuclear fractions. There 

 was a différence from the normal pattern in regenerating rat liver after 

 partial hepatectomy. 



The incorporation of labeled amino acids into proteins and an jincrease 

 in protein nitrogen wereobserved also on the isolated nuclei of calf thymus 

 and transplanted rat sarcoma "Mj" incubated in vitro with a mixture of 

 amino acids and a factor produced by mitochondria. 



On the basis of the results presented it may be concluded that cell 

 nuclei produce mostly spécifie proteins and nucleoproteins, determing nor- 

 mal cellular development and differentiation. 



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