VII. SYNTHESIS OF RNA AND RIBOSOMES 



293 



and the RNA-rich j)articles as well as any protein which was sedimented 

 by the prolonged centrifiigation, the rejjorted composition of the micro- 

 somes was highly variable. In 1957 the term "ribosome" (originally 

 suggested by H. M. Dintzis) was introduced to distinguish the particu- 

 late material from the remainder of the microsome fraction (Roberts, 

 1958). 



B. EFFECTS OF MAGNESIUM 



In the same year the effect of magnesium concentration upon the 

 sedimentation coefficients obtained for the ribosomes was recognized. 

 Chao showed that the larger ribosomes (about SOS) obtained from yeast 



Exponential (broth) E. CoU 



Fig. 1. Centrifugation pattern of juice from E. coll growing in broth medium. 

 These rapidly growing cells have a high content of ribosomes. Sedimentation from 

 left to right observed in Spinco Model E ultracentrifuge. 



