VII. SYNTHESIS OF RNA AND RIBOSOMES 



319 



70S 50S 30 S 



^ i I 



,,s 70S SOS 



(b) ^ I 



3xlO"'M 



30S 



CL 



30 40 



Fraction number 



Fig. 15. Sedimentation analysis of a total extract from cells labeled with P'' for 

 four generations and with C"-uracil for 2 minutes. Cells washed and extracts 

 prepared and run in tris-HCl 0.01 M, pH 7.4 (a) containing MgCL at 10"= M, (b) 

 3 X 10'' M, (c) 10"' Af, (d) WM. Centrifugation : (a), (b), and (c) 90 minutes at 

 37,000 rpm; id) 150 minutes at 37,000 rpm, 4°C. 



