IV. CELLULAB CONTROL OF DNA BIOSYNTHESIS 



177 





o 

 o 



10 20 30 40 50 



UNITS DNA 



Fig. 8. Microspectrophotometric distribution of the DXA content of individual 

 I. cells (clone P2) grown for 48 hours in (A) complete medium, (B) medium from 

 wliich leucine was omitted, and (C) medium from which glutamine was omitted 

 (10 units of DNA equal to approximatelj^ 4 fifig). In the absence of either leucine or 

 glutamine nuclei accumulate which cannot double their DNA complement. (Unpub- 

 lished data of Dr. J. Paul printed here by his kind permission.) 



and protein synthesis could be achieved by simply prolonging the period 

 of uracil starvation, and again no diminution of DNA synthesis was 

 observed (in both cases synthesis of DNA was greater than 600% of the 

 initial intracellular content). As an example of a possible type of ex- 

 planation which could be advanced, the authors pointed out that amino 

 acid-conjugated deoxynucleotides might be required for DNA synthesis. 



