a 



b 



EXP. NO. 



GENERATIONS 



0.3 



0.7 



1.0 



I.I 



1.5 



1.9 



2.5 



3.0 



4.1 



Oandl.9 

 mixed 



Oond 4. 

 mixed 



Fir;. 3. ((/) I'ltraviolet absorption photograpli.s .showing DXA hand.s rrsulting 

 from density-gradient centrifugation of ly.sates of E. cuh .sampled at various times 

 after the addition of an e.xcess of N^ substrate to a culture of cells labeled with 



78 



