226 



CELL HEREDITY 



200 400 



UV Dose (seconds) 



(2536 A) 



30 50 100 200 



30 50 100 200 



Dose (seconds) 

 (2536 A) 



30 50 100 200 



FIGURE 8.15. Reversal of the effects of ultraviolet light by visible light in E. coli 

 (from Novick and Szilard, 1949, Proc. Nail. Acad. Sci. Wash., 35:591). 



shows, the immediate synthesis of a new protein; a few minutes later 

 phage DNA begins to increase in amount. If chloramphenicol is present 

 at the time of infection, neither compound is synthesized until the 

 chloramphenicol is removed. But if it is added 5 minutes after infection, 

 when protein synthesis has already begun, then DNA formation will take 

 place even though protein synthesis does not continue. Some protein 

 synthesis seems to be a prerequisite for DNA synthesis. This protein 

 has been shown by isotope tracer experiments not to be a precursor of 



