W. S. VINCENT 



11 



and uracil content between nucleolus and cytoplasm. Of interest 

 here is the fact that the purine-pyrimidine ratio of the cytoplas- 

 mic RNA is 1:1, while the nucleolar RNA varies considerably 

 from this ratio. The cytoplasmic RNA of animals generally seems 

 to follow the pattern found in the starfish of high guanine and 

 cytosine values, and a purine-pyrimidine relationship of unity. 

 Nuclear RNA's, on the other hand, depart from this relationship 

 (Elson and Chargaff, 1954). 

 Radioisotope Studies on Nuclear RNA. Numerous reports of 



40 r 



30 



20 



14C 



30 



20 



-10 



GUANINE ADENINE CYTOSINE URACIL 



Fig. 5. Moles of nitrogenaus base per 100 moles of phosphorus in RNA 

 isolated from Asterias ruhens nucleoli (dotted) and cytoplasmic granules 

 (shaded). (Recalculated from Vincent, 1952.) 



rapid synthesis of RNA by nuclei have appeared in the last few 

 years (see Smellie, 1955, for review). I have carried out a series 

 of studies on the metabolism of RNA in the starfish oocyte in 

 which radiophosphorus was used as the tracer element. The ova- 

 ries of the starfish are removed, the gonoducts are tied off and 

 then placed in filtered sea water containing inorganic P^^ at ap- 

 propriate levels. The usual dosage has been about 0.25 microcurie 

 of P^" per milliliter of sea water. After exposure for appropriate 

 intervals, the ovaries are removed, washed thoroughly in filtered 

 sea water, and the nucleoli and other fractions are isolated. Some 



