ROBERTS, BRITTEN, AND BOLTON 



89 



centrifuged (100,000^, 2 hours), a colorless glassy pellet is formed which con- 

 tains approximately 65 per cent of the protein and nucleic acid. This pellet 

 resuspends easily and completely. The analytical centrifuge shows that it con- 

 tains peaks in the 20 to 40 S region, whereas the 80 S peak was most promi- 

 nent in the original material. The ratio of nucleic acid to protein in this pellet 

 (measured by optical density at 260 mu and S 35 ) is twice that of the starting 

 material, and the elution pattern obtained when the pellet is rerun on a DEAE 

 column is very different (fig. 5). 



These changes appear to be caused by the column material and not by the 

 salt of the eluting fluid. Ribosomes exposed to molar NaCl show a reduction 

 in size but no change in composition or elution pattern. 



The fractionation and analysis procedures outlined above are beginning to 

 yield some useful information about the composition and function of the ribo- 

 somes. The purified ribosomes are markedly different from the microsome 

 pellet. For example, the microsome pellet contains considerable phospholipid 

 (table 1); the ribosomes, little if any. Moreover, the nucleic acid to protein ratio 

 is somewhat variable in the crude microsome pellet, but the purified ribosomes 



16 20 24 



Column fraction no. 



28 32 36 40 



Fig. 5. 

 change to 



Nucleoprotein peak of elution pattern spun down and rechromatographed. Note 

 elution pattern like that of nucleic acid. 



