310 



R. U. ROBERTS, R. J. BRITTEN, AND B. J. MCCARTHY 



- 600 



- 400 



- 200 



E 

 O 

 CVi 



050 - 



I 



- 2400 



- 1600 



-800 £ 



- 10.000 



- 5000 



40 50 



Fraction number 

 Fig. 13. Analysis of total ribosomal pellets (40K 240 minute pellets) on a 

 DEAE-cellulose column. Linear sodium chloride gradient from 0.2 3/ to 1.2 M in 

 tris-HCl buffer 0.01 M containing MgCL 0.01 M, pH 7.4. Salt gradient 0.004 M/ml 

 Volumes collected 3.6-3.8 ml. (a) 25 seconds exposure to C"-uracil, (6) 50 seconds, 

 (c) 100 seconds, (d) 3 minutes, (e) 6 minutes, (/) 12 minutes. The three sequentially 

 labeled peaks appear at 0.6 M, 0.5 M, and 0.4 M NaCl. 



quantitative analysis given below (Section V,D). As these two pre- 

 cursors have quite distinct elution properties, as well as other charac- 

 teristics to be described later, we have used the names "eosome" and 

 "neosome" to distinguish them from ribosomcs and to indicate their 

 order in the sequence of synthesis. 



B. SEDIMENTATION ANALYSIS 



Most of the earlier studies of the kinetics of ribosome synthesis were 

 carried out by means of sedimentation analysis in a magnesium concen- 



