W. S. VINCENT 15 



The possibility exists that the higher isotope content of nucle- 

 olar RNA is due to contamination by a small fraction of highly 

 active material other than RNA. Although such a possibility has 

 not been totally eliminated, the procedure used for extraction of 

 RNA (Vincent, 1952) has been highly satisfactory in giving very 

 good separation of this compound. Ultraviolet absorption meas- 

 urements and dii'ect phosphorus determination have been made 

 in every case. The two types of preparations are handled in iden- 

 tical fashion, but agreement between the two has been found to 

 be within the limits of experimental error. This procedure in- 

 cludes thorough washing in cold O.IIV HCl and 60 minutes reflux- 

 ing in boiling alcohol-ether prior to extraction of RNA in hot iV 

 acid. On the basis of these considerations it seems likely that the 

 increased activity present in sucrose nucleoli must be present in 

 a small fraction of the RNA. This fraction is apparently lost in the 

 distilled water media. 



Structural and Soluble RNA. The data given here are inter- 

 preted as follows. The nucleolus of the starfish oocyte contains at 

 least two types of RNA. One type is bound to the nucleolar struc- 

 ture and has been characterized thus: it is most of the RNA pres- 

 ent in the nucleolus; it is resistant to removal by water solutions; 

 its base ratio differs from the cytoplasmic RNA in guanine and 

 uracil content; it is metabolically relatively inactive. This is called 

 structural RNA. The other RNA is characterized primarily from 

 inference. It appears to be soluble in distilled water; to be pro- 

 duced in amounts related to cytoplasmic synthetic activities; and 

 to be synthesized at a rapid rate, in that it contains nearly all the 

 label in isotope experiments. Its base composition is as yet un- 

 known. This RNA fraction has been designated soluble RNA. 

 ( See Vincent, 1955a, for a more extensive discussion of nucleolar 

 RNA.) 



Functions of Nuclear RNA 



I should like to suggest some possible functions for these RNA 

 fractions. The nucleolus contains the highest concentration of dry 

 matter (predominantly protein) of any cell structure (Vincent, 

 1955a ) . A suggested role for the structural RNA is that it precip- 



