14 



THE OOCYTE 



of recovered isotope within the nucleokis and cytoplasm a more 

 striking picture appears. As shown in Fig. 7B, at 2 hours, 75% 

 of the total radiophosphorus present in the nucleolus is in the 

 RNA fraction. A more extensive analysis of the time distribution 

 of radiophosphorus in nucleoli is in progress, but the very high 

 proportion of radiophosphorus present in the RNA fraction at the 



J5 



< 5 



A 



SUCROSE 



isolationkI^ 



HjO ISOLATION 



2 4 



Hours 



80 



60 



40 



20 



Bo 



NUCLEOLAR RNA 



CYTOPLASMIC RNA 



3..^-'' 



4 

 Hours 



Fig. 7. A. Comparison of relative specific activities of nucleolar and 

 cytoplasmic RNA when nucleoli were isolated in Ca-sucrose (solid line) 

 and in distilled water (dashed line). B. Per cent of total counts recovered 

 from nucleoli and from cytoplasm which was found in the RNA fraction. 



short time interval strongly suggests that RNA synthesis occurs 

 in, or immediately adjacent to, the nucleolus. 



Another fact which has emerged from these studies on isolated 

 nucleoli is that the RNA concentration (3.6% for H-O, 3.97c for 

 sucrose, range identical) is not significantly different in the nu- 

 cleoli isolated by the two different techniques, although very sig- 

 nificant differences in radioactivity of RNA in the two different 

 preparations are apparent, 



