VII. SYNTHESIS OF RNA AND RIBOSOMES 321 



Finally, the C'^-uracil accumulates in the end products, the 308 and 

 50S ribosomes. In addition, radioactivity builds up in S-RNA which 

 sediments at 4S. A qualitative comparison with the sequence of events 

 revealed by DEAE chromatography suggests that the first precursor, 

 eosome, sediments at 14S and that neosomes are present in both the 43S 

 and the 308 regions. The 308 and 508 ribosomes correspond to the main 

 ribonucleoprotein peak of the column analysis. 



C. QUANTITATIVE KINETIC ANALYSIS 



To compare the results of experiments with theoretical models the 

 experimental data are expressed in terms of functions ^.v. These functions 

 and the other needed symbols are defined below. 



r: Time after addition of tracer; units such that t = 1 when 

 the cells have grown by a factor e; Q = Q^e'' gives the growth 

 of the cells or any components. 

 m: Effective specific radioactivity of tracer; units such that the 

 specific radioactivity of the RNA will approach m after a 

 long period of growth at a constant tracer concentration. 

 X: Quantity of a component, in general. 

 X* : Its radioactivit3^ 

 fix'. Its specific radioactivity. 

 E, N, R: Quantities of three specific components. 

 T: The total of all components. 



«.v=^-| = ^ (1) 



This choice of units is designed to allow different experiments carried 

 out with different growth rates and different effective tracer radioactivi- 

 ties to be plotted on the same graph. 



While ^A is adequately defined by Eq. (1), the following general 

 definition may perhaps be useful, ^.v is the ratio of the number of labeled 

 atoms at a given time in a given class of molecules to the number of 

 atoms in the whole cell which would be labeled after a long period of 

 growth during which the labeling conditions were precisely constant, 

 ^.v is thus a measure of the number of newly synthesized molecules which 

 occur in a given class, and has been named the "newly" synthesized 

 fraction." 



When there are two sequential precursors (E and N) to a product R 



