The preparation of ribosomes and ribosomal subunits from Xenopus ovary is described. 2. The yield of once-washed ribosomes (buoyant density in caesium chloride 1.601g.cm(-3); 44% RNA, 56% protein by chemical methods) was 10.1mg/g wet wt. of tissue. 3. Buoyant density in caesium chloride and RNA/protein ratios by chemical methods have been determined for ribosome subunits produced by 1.0mm-EDTA or 0.5m-potassium chloride treatment and also for EDTA subunits extracted with 0.5m-, 1.0m- or 1.5m-potassium chloride, 4. Analysis of ribosomal protein on acrylamide gels at pH4.5 in 6m-urea reveals 24 and 26 bands from small and large EDTA subunits respectively. The actual numbers of proteins are greater than this, as many bands are obviously doublets. 5. Analysis of the proteins in the potassium chloride extract and particle fractions showed that some bands are completely and some partially extracted. Taking partial extraction as an indication of possible doublet bands it was found that there were 12 and 20 such bands in the small and large subunits respectively, making totals of 36 and 46 proteins. 6. From the measured protein contents and assuming weight-average molecular weights for the proteins of large and small subunits close to those observed for eukaryote ribosomal proteins it is possible to compute the total numbers of protein molecules per particle. It appears that too few protein bands have been identified on acrylamide gels to account for all the protein in the large subunit, but probably enough for the small subunit.
