VII. SYNTHESIS OF RNA AND RIBOSOMES 307 



TABLE III 

 Properties of E. coli Ribosomes" 



Key: S, sedimentation coefficient S^.w X 10^^ cm/sec; D, diffusion coefficient 

 D20.W X 10^ cmVsec; V, partial specific volume; 77, viscosity cm/dl; MW, molecular 

 weight X 10-8. 



" From Tissieres et al. (1959). 



* Calculated from S and D. 



" Calculated from S and rj. 



Electron microscopy of purified ribosome preparations provides the 

 dimensions shown in Table IV (Hall and Slayter, 1959; Huxley and 

 Zubay, 1960). 



Electron microscopy of sectioned bacteria is more ambiguous. Some 

 sections show dense regions which may be due to ribosomes, others which 

 might be expected to show ribosomes do not. It is not at all clear whether 

 these differences are due to differences in staining techniques or whether 

 the ribosomes do not exist as compact spheres in the living cell (Hanzon 

 ef a/., 1959). 



The protein/nucleic acid ratio of 37/63 corresponds closely to a 

 ratio of 2 amino acids/nuclcotide. Furthermore, a portion of the protein 

 can be removed (see Section III,A) leaving another portion still in the 

 ribosome structure. Electron microscopy of ribosomes stained with uranyl 

 acetate shows no evidence of a protein shell around a nucleic acid core 

 (Huxley and Zubay, 1960). These findings suggest that the 2/1 ratio 

 may not be fortuitous but a consequence of saturating the entire RNA 

 strand w4th protein along its entire length. 



The hyperchromicity of ribosomes is 40%, the same as that of the 

 RNA after isolation from the ribosomes. Thus, some aspects of the RNA 

 structure are not appreciably altered by the addition of protein (Schles- 



