PETERMANN ET AL. 73 



picture down, chiefly B. After dialysis overnight against bicarbonate contain- 

 ing 0.005 M MgCl 2 the RNP is unchanged. With less magnesium, as shown 

 in the two upper pictures, it dissociates; with more magnesium, as shown in 

 the bottom row, the B boundary gets smaller, because the RNP has begun to 

 aggregate and precipitate out. 



In the purified RNP we found 40 per cent RNA on a dry-weight basis [9]. 

 Similar values have been found for purified RNPs from yeast [10] and pea 

 seedlings [11], again on a dry-weight basis. When RNA is compared with 

 protein nitrogen, on the other hand, we and many other workers find values 

 for RNA of 50 to 60 per cent. Some of this discrepancy is probably caused by 

 lipid, which contributes more to the dry weight than to the nitrogen. Some of 

 it, however, seems to occur because hot 5 per cent trichloroacetic acid extracts 

 some other nitrogen besides that in the RNA. With 10, 15, and 20 per cent 

 trichloroacetic acid we still find extra nitrogen in the extracts. 



A B E S P H NaHC0 3 Phos. MgCI 2 



+ + + + M MM' 



V 



82 O.IO O.OOI 



8.2 O.IO O.OOI 0.0005 



8.2 0.10 0.001 0.0050 



8.2 0.10 0.001 0.0100 



Fig. 3. The effect of magnesium on the stability of purified RNP. Ultracentrifugal 

 patterns were obtained after 14 minutes at 37,020 rpm. 



We have carried out a number of metabolic studies on purified RNP con- 

 taining about 4 per cent ferritin. Figure 4 shows the incorporation of glycine- 

 1-C 14 into adenine and peptide glycine. The upper row shows the time course 

 of the incorporation in normal male rats. Fifteen minutes after the injection 

 of the isotope, by tail vein, the specific activity of the acid-soluble adenine of 

 the liver was quite high, whereas that of the adenine in the purified RNP was 

 still very low, and, although it increased very slowly with time, it was still low 

 at 17 hours. The specific activity of the liver nucleoprotein glycine was highest 



