RNA IN THE SYNTHESIS OF PROTEINS 



various protein components found in the total population. But so far, all 

 attempts by Dr. Waller to separate chromatographically intact ribosomes 

 into fractions with different starch-gel patterns have failed. The total protein 

 component of a 70s ribosome amounts to about 9 X 10 5 daltons. Since the 

 end group analysis suggests an average mol. wt. of about 30,000, approx- 

 imately 20 polypeptide chains are used in 50s construction and 10 for the 

 3 os ribosome. It is possible that all the polypeptide chains in a 30s particle are 

 different. Waller already has evidence for 10 distinct components in 30s 

 ribosomes and the present failure to observe more in the 50s protein fraction 

 may merely mean that the same electrophoretic mobility is shared by several 

 polypeptide chains. 



We believe that all these proteins have primarily a structural role. That is, 

 they are not enzymes but largely function to hold the ribosomal RNA and 

 necessary intermediates in the correct position for peptide bond formation. 

 In addition a number of enzymes are bound tightly to ribosomes. As yet 

 their function is unclear. One such is a bacterial ribonuclease, found by 

 Elson 21 to be specifically attached to 30s ribosomes in a latent form. No 

 ribonuclease activity is present until ribosome breakdown. Dr. Spahr 22 in our 

 laboratories has purified this enzyme, shown its specificity and from specific 

 activity measurements, concludes that it is present on less than one in twenty 



RNA 



MW x 10 



16 S 

 0.55 ± 0.10 



2(16S) 



Fig. 3. Molecular weights of RNA isolated from E. coli ribosomes. (This picture is 

 diagrammatic and does not represent the true conformation of ribosomal RNA.) 



s-117 



