VII. SYNTHESIS OF RNA AND RIBOSOMES 



331 



by the degradation of a part of the high molecular weight RNA fraction. 

 Thus if the D-RNA portion of the eosome fraction were degraded after 

 an average lifetime of some 2 minutes, the delay in labeling could reflect 

 the utilization of these secondhand nucleotides for S-RNA and DNA 



synthesis. 



3000 - 



a; 



"^ 2000 



c 



=5 

 O 



o 



CVI 



ro 

 CL 



1000 



- 600 



400 



- 200 



Z5 



o 

 o 



100 



200 



300 



Mi. Eluote 



Fig. 23. Chromatography on a column of protein-coated kieselguhr of phenol- 

 prepared nucleic acids from E. coli labeled randomly with P^^Or'" and for 1 minute 

 with C"-uracil. Elution with a linear gradient of NaCl in 0.04 M phosphate buffer, 

 pH 6.7, from 0.4 3/ to 1.1 M. Flow rate 35 ml/hour. 



In support of this view is the fact that the delay in S-RNA and 

 DNA labeling by C^*-uracil is abolished by the presence of chloram- 

 phenicol. Under these conditions, where C"-uracil accumulates in the 

 eosome fraction (see Section VII), nucleotide analyses indicate that 

 D-RNA is synthesized but degradation is markedly reduced (Midgley, 

 1962). There is then little transfer of label from D-RNA to S-RNA 

 and DNA. 



VII. Kinetics of Incorporation into Protein 



A. INCORPORATION OF C"-LEUCINE INTO THE RIBOSOMES 



The separation of ribosomes from their precursors by chromatogra- 

 phy depends, presumal)ly, on differences in their proportions of protein. 

 Thus it appears that the product ribosomes are not formed by accretion 

 of material having a constant nucleic acid/protein ratio but that the 

 addition of RNA and protein occurs in time separated stages. J\Iore 



