W. S. VINCENT 17 



the synthesis of new material genetic guidance. As it has been 

 shown that the synthesis of both RNA and specific protein will 

 occur in the absence of the nucleus, although at a diminished 

 rate (Brachet, 1955), one can question the necessity of the nu- 

 clear contribution to synthetic activities. The intimate correlation 

 of nucleolar activities with cytoplasmic synthesis however (see 

 above, also Vincent, 1955a) necessitates the presumption of some 

 sort of relationship between nuclear, nucleolar, and cytoplasmic 

 activities. The finding of Baltus that nucleoli possess high con- 

 centrations (although less than 10% of the cellular activity) of 

 nucleoside phosphorylase and DPN synthetase certainly suggests 

 that the nucleolus can be involved in nucleotide synthesis. The 

 autoradiographic results mentioned above, and the data reported 

 in this paper strongly suggest that RNA synthesis itself occurs in 

 the nucleolus. 



The data on the RNA of nucleolus and cytoplasm raise another 

 problem in that the base content of the two regions differs widely. 

 Such a difference is found in the starfish (in Fig. 3). This is not 

 in agreement with the hypothesis that nuclear or nucleolar syn- 

 thesis is the sole source of cytoplasmic RNA. The experiments 

 presented above, however, strongly indicate the presence of at 

 least two metabolically quite different RNA fractions in the nu- 

 cleolus. Further characterization of these fractions may help to 

 resolve this apparent disagreement. 



We are then faced with the conclusion that the chromosomes, 

 the nucleolus, and the cytoplasm are all able to carry out de novo 

 synthesis of RNA. Accepting the contention that specificity is 

 conferred on RNA from a DNA template and that this RNA 

 passes to the cytoplasm, we know that this specificity is main- 

 tained for some time in the cytoplasm (Hammerling, 1953). 

 Whether or not the cytoplasm is able to reduplicate specific RNA 

 molecules (i.e., the plasmagene hypothesis of Spiegelman and 

 Kamen, 1946), has not yet been adequately determined. Enucle- 

 ation experiments suggest that if the cytoplasm is able to perform 

 this function, reduplication is not able to keep up with destruc- 

 tion, and therefore the system eventually runs down. 



We have mentioned two possibilities for RNA synthesis in the 



