W. S. VINCENT 



13 



The sucrose procedure mentioned above was then developed 

 in an attempt to maintain a higher integrity in the isolated nucle- 

 oli. The results of the experiments after isolation in sucrose media 

 are compared with the results obtained in pure water isolation in 

 Figs. 6 and 7. The results obtained from these studies compare 

 favorably with those obtained by Ficq ( 1953, 1955 ) in radioau- 

 tographic studies of starfish nucleoli. Ficq, using a value of 10% 

 RNA for cytoplasm, calculated a relative specific activity of nu- 

 cleolar RNA of 100 X that of the cytoplasm. This value, taken 



a. z 



SUCROSE ISOLAIION 



H2O ISOLATION 



4 

 Hours 



Fig. 6. Specific activity of nucleolar phosphorus after isolation in dis- 

 tilled water and in Ca-sucrose solutions. 



from Vincent (1952), was for the mixed mitochondrial-micro- 

 some granules of the oocyte cytoplasm. Actual values found for 

 RNA concentration of acetone-dried starfish cytoplasm average 

 1.7% (range l.l%-2.5%). Ficq's value of lOOX should thus be 

 reduced by a factor of at least 5, which brings the values found 

 by radioautography into reasonable agreement with those found 

 by direct analyses of isolated nucleoli. 



These data are in agreement with the findings of other workers 

 that nuclear RNA appears to accumulate radiophosphorus more 

 rapidly than cytoplasmic RNA. If one examines the distribution 



