W. S. VINCENT 9 



nucleoli possess a RNA fraction which is readily soluble in distilled 

 water. 



A summary of some of the data on nucleolar RNA is given in 

 Fig. 2. Here the data are plotted against oocyte diameter and 

 related to the changes in cytoplasmic volume which are shown 

 on the lower part of the figure. In general, one finds that the 

 oocyte enters a new phase of activity at about 100 microns, with 

 the onset of rapid cytoplasmic growth. This can be attributed to 

 the synthesis of yolk proteins. This new phase of activity is re- 

 flected also in a drop in cytoplasmic RNA concentration not 

 shown here, but readily apparent on slides stained with basic 

 dyes. Such a cytoplasmic picture is typical of oocytes (Vincent 

 and Dornfeld, 1948; Brachet, 1950; Panijel, 1951; Dalcq and 

 Van Egmond, 1953 ) . The nucleolar changes which precede cyto- 

 plasmic synthesis are of considerable interest ( Fig. 2 ) . In general 

 one finds a shifting from curvilinear to linear relationships. RNA 

 concentration drops very rapidly during early growth of the oo- 

 cyte, but with the onset of the production of constant amounts 

 of soluble RNA, maintains a constant concentration, although the 

 nucleolus continues to grow. The nucleolus stops growing shortly 

 after the onset of yolk deposition. 



RNA Metabolism in Starfish Oocytes 



By studying isolated nucleoli it has been possible to obtain 

 some information about the metabolism of RNA in the oocyte 

 nucleus. The advantages of working with pure preparations of 

 isolated cell organelles are well known, and therefore a technique 

 was developed whereby nucleoli could be isolated in quantity 

 from starfish oocytes (Vincent, 1952). Distilled water was used 

 as an isolation medium. Baltus (1954) reported that a modified 

 technique in which sugar solutions of high density were used 

 gave greater biochemical integrity than the distilled water me- 

 dium. The technique was tedious and the yield low, however. 

 The results and interpretations reported below are based prima- 

 rily on studies carried out on nucleoli isolated in a Ca-sucrose 

 medium. This process was developed when it became apparent 

 that RNA was lost from the nucleoli into the distilled water iso- 



