LYSOGENY 379 



in B. megaterium (lonesco, 1953), synthesis of antigens in Sal- 

 monella (Iseki and Sakai, 1953), or capacity to reproduce various 

 unrelated phages (Anderson and Felix, 1953b; Bertani, 1953b). 

 Although a prophage does not interfere with the reproduction of 

 unrelated phages in general, it does alter the susceptibility of 

 the bacterium to particular phages. The prophage lambda 

 confers on E. coli K12 the ability to distinguish between dif- 

 ferent mutants of phage T4 (Benzer, 1955). This phenomenon 

 reflects the existence of a phage-specific block in multiplication 

 of infecting particles interposed by the presence of the prophage. 

 In other cases, the prophage plays a role in the phenomenon of 

 host induced modification of superinfecting phage (Chapters 

 XVI and XXI). 



Many examples of interference by a prophage with the multi- 

 plication of an unrelated phage are now known. Many of 

 them were discovered among the typing phages used to dis- 

 criminate different strains of a single bacterial species. In 

 most instances this interference is an expression of complex 

 interactions at the intracellular level, of which the outcome is 

 determined by the genetic specificity of all three components, 

 namely, the bacterium, the prophage, and the superinfecting 

 phage, and even sometimes by a fourth factor, the particular 

 modification of the superinfecting phage imposed on it by the 

 bacterium from which it issued. Specific examples of this kind 

 are presented in Chapter XXI. 



9. Conclusion 



Lysogeny presents a remarkable situation in which the re- 

 lationships between virology and genetics, dimly seen in previ- 

 ous chapters of this book, are clearly illustrated. Certain phages 

 called temperate can multiply like typical viruses, bringing about 

 the destruction of the cells they infect. Alternatively they can 

 establish a stable association with the surviving host, to be 

 perpetuated in a nonpathogenic form called prophage. Once 

 established as prophage, the genetic material of the phage is 

 integrated in a specific manner with the genetic material of 



