BIOLOGICAL ORDER 



nfection 



20°, Chloromycetin, starvation 40°, U.V, 



lysogenizotion 



' X X X X ^ ^ 



X V X X 



X ^ X X X X 



X X 



X y 



X ^. X 

 X X X X X 



vegetative phase 



•\AAAphQge D. N. A. ^ phage proteins 



X repressor 



Figure 31. The Fate of the Infected Bacterium. 



The nonlysogenic bacterium is infected: 



1-3: at low temperature (20°C.) in the presence of chloramphenicol, or in 

 bacteria deprived of food, the first activity of the genetic material of the 

 repressor. As a consequence the synthesis of phage protein is repressed, the 

 vegetative phase is not initiated, and the genetic material of the phage reaches 

 its chromosomal locus and becomes a prophage. 



4-5: at high temperature (40°C.), or in a bacterium irradiated with ultra- 

 violet rays. The first activity of the genetic material of the phage is the synthesis 

 of a protein. The vegetative phase is initiated, and infectious particles are 

 produced. 



with ultraviolet light, although all other characters of the mutant 

 were the same as those of the original strain. The mutant not induci- 

 ble with ultraviolet light is, however, sensitive to zygotic indu<iition. 

 Double lysogenic strains can be obtained that carry two prophages A: 



[76] 



