820 



R. B. ROBKRTS, R. J. HRl'ITKN, AND B. J. MCCARTHY 



gCf^ti'd that tlicsf cDiiditions of cell breakage and analysis of extracts 

 would be suitable for the determination of the details of the kinetics of 

 ribosome synthesis. 



Therefore, analyses were made in 10 ' M magnesium of six samples 

 of extracts prepared from P'*- steady-state labeled cells given from 30 



10 20 30 40 



10 20 30 40 



Fraction number 



- 600 



400 



200 



3000 



- 2000 



1000 



10 20 30 40 



Fig. 16. Sedimontation analy.sis uf six DNawe treated total extracts made and 

 centrifuged in tris-HCl 0.01 M, pH 7.4, MgClj 10 ' M from cells steady state labeled 

 with P" given (a) 30 seconds' exposure to C"-uracil, (b) 1 minute, (c) 2 minutes, 

 (d) 4 minutes, (e) 7 minutes, (/) 10 minutes. Centrifugation : 175 minutes at 37,000 

 rpm, 4°C. 



seconds to 12 minutes' exposure to C'^-uracil (Fig. 16). The extracts 

 were treated with DNase prior to centrifugation. The P^" profile shows 

 three main peaks of 50S and 308 ribosomes and soluble RNA. 



The patterns indicate a sequence of precursors and products. At the 

 earliest time the C^^-uracil is carried by material sedimenting in a broad 

 band centered at about 14S. Later, C'^-uracil shows at 30S and at 438. 



