16 THE OOCYTE 



itates nuclear proteins, and aids in bringing about this very dehy- 

 drated state. The soluble RNA, produced at a rapid rate and be- 

 ing quite soluble, is apparently passed to the cytoplasm. Its ap- 

 pearance and amount suggest that it is intimately associated with 

 protein synthesis. These qualities are those required of a material 

 which could transfer genetic specificity to the cytoplasm. 



The data given here will not distinguish between the two al- 

 ternatives, (a) RNA is synthesized within the nucleolus, and 

 ( b ) RNA is synthesized elsewhere in the nucleus and specifically 

 accumulated by the nucleolus. The paper of Taylor et al. (1955) 

 offers a possible answer to this problem, at least in the material 

 which they used (Drosophila). They found that with high reso- 

 lution radioautographs P^- appeared to be localized initially (1 

 hour after feeding of the isotope) immediately adjacent to the 

 nucleolus, possibly associated with the chromosomes. This sug- 

 gests that the RNA was initially synthesized adjacent to or on the 

 surface of the nucleolus. Within two hours, the label appeared 

 to be evenly distributed in the nucleolus. They found no appar- 

 ent localization of activity about a single region, as would be ex- 

 pected if the nucleolus organizer region were the sole site of 

 synthesis of nucleolar materials. (For a discussion of the origin 

 of nucleolar materials, see Vincent, 1955a. ) 



The work of Goldstein and Plaut ( 1955 ) also supports the con- 

 tention that RNA is actually synthesized in the nucleus. Their 

 results appear to demonstrate the passage of the label on RNA 

 from the nucleus of the amoeba to the cytoplasm, but no reverse 

 passage appears to occur. Such data seem to be best interpreted 

 by concluding that RNA is synthesized in the nucleus and passes 

 to the cytoplasm. On the other hand, cytoplasmic RNA does not 

 appear to move in the reverse direction. 



A further question arises in considering the role of the nucle- 

 olus in RNA relationships between nucleus and cytoplasm. Is the 

 nucleolus at all necessary in a system of specificity transfer such 

 as has been suggested? If specificity residing in DNA is trans- 

 ferred to RNA structure by a template mechanism of synthesis 

 (Bounce, 1953; Lockingen and DeBusk, 1955), the RNA product 

 could then diffuse diiectly to the cytoplasm and there impart to 



