Chapter 3 



The Role of the Cell Nucleus in RNA and 

 Protein Synthesis 



1. HYPOTHESES ON THE BIOCHEMICAL ROLE OF THE NUCLEUS 



Many hypotheses concerning the biochemical role of the cell nu- 

 cleus have been disproved experimentally. For instance, it is no 

 longer held that the nucleus is the main center of cellular oxidations, 

 as Loeb believed in 1899, or that it is a ''storehouse" of enzymes, 

 as Wilson concluded in 1925. Removal of the nucleus, in many 

 cases, has no appreciable effect on the oxygen uptake and few en- 

 zymes are more concentrated in the nucleus than in the cytoplasm 

 (see Brachet, 1957, for a full discussion of these problems). 



More satisfactory is the view already held in 1892 by Verworn 

 that the nucleus is the center of the synthetic activities of the cell, i.e. 

 of its anabolism. Verworn's (1892) idea has been made more pre- 

 cise by Caspersson (1941, 1950), who considers the nucleus as a 

 cell organelle especially organized as the main center for the for- 

 mation of proteins. Caspersson's(1941, 1950) theory is based espe- 

 cially on his own cytochemical observations, which established that 

 the nucleolus is well developed and rich in RNA in all cells which 

 are the sites of intensive protein synthesis. This finding has since 

 been abundantly confirmed. According to Caspersson (1941, 1950), 

 cytoplasmic RNA accumulates around the nuclear membrane ; that 

 such a perinuclear accumulation of RNA is a universal phenome- 

 non appears somewhat doubtful now. 



More recently, Mazia (1952) proposed the new hypothesis that 

 the nucleus is concerned with the replacement of the activities of the 

 cell. Mazia's (1952) hypothesis is based on the essentially correct 

 observation that removal of the nucleus is not followed by imme- 



