334 



R. B. KOHEHT; 



HUITTEN. AND B. J. MCCARTHY 



800 - 



—^ 600 - 



c 



o 

 o 



(M 



ro 



400 - 



200 



- 4000 



- 3000 



- 2000 ^ 



- 1000 



c 



o 

 o 



o 



20 30 



40 



Fraction number 



Fig. 26. The effect of chloramphenicol on the incorporation of C"-uracil into 

 ribosomes. Cells were grown for three generations in P^" and given a 10-minute 

 exposure to C"-uracil. (a) Control, (h) in the presence of chloramphenicol (200 

 fig/ml added 2 minutes before the uracil). Cells washed and extracts prejiared in 

 tris-HCl 0.01 M. pH 7.4, MgCL 10' i1/ in the iircsence of DNase. Ccntrifugation 160 

 minutes at 37,000 rpm, 4°C. 



estimates made from the two leucine exi)eriinents suggest that the 43S 

 has a protein to RNA ratio 14 to Ys t^^'^t of the 50S ribosome. 



The final flow diagram, including both RNA and protein moieties of 

 ribosomes, is shown in Fig. 27. The open and shaded areas are propor- 

 tional to RNA and protein contents. The eosome is shown as pure RNA 

 since there are no measurements of its protein content. The 30S neosome 

 is shown with less than half of the ])rotein of the 30S ribosome by 

 analogy to the 43S. This point is not really established because of the 

 lack of resolution between objects in the 30S size range. Likewise, the 

 30S neosome which is precursor to the 43S is shown as a sej)arate object 

 and this may well be an unnecessaiy complication. The 43S neosome is 

 shown with only one-quarter of the protein of the 50S ribosome. This 

 quantity is uncertain and it is not known what fraction of its protein 

 enters directly in the formation of the 438 or by way of the 30S 

 precursor to it. While these estimates of relative protein contents in 

 neosome and ribosome are crude and preliminary, it is clear that con- 

 version of neosome to ribosome involves only the addition of protein antl 

 that the greater part of the ribosome protein is added in this step. 



