Metapolefic Integrations IS 



to be the result of the integration of the genetic material 

 of the bacterium and of the bacteriophage, an integration 

 which produces modifications and will therefore be called 

 "metapoietic" (generating changes). 



A few examples will be given to exemplify the notion of 

 interaction of the genetic materials of the two partners of 

 the lysogenic system. Then, some typical cases of meta- 

 poietic integrations will be described and the theoretical 

 implications of the phenomena discussed. 



Inducibilify 



In some lysogenic systems the development of phage from 

 prophage is initiated by an appropriate treatment, such 

 as irradiation with ultraviolet light. In other systems the 

 probability of phage production cannot be, or at least has 

 not yet been, modified. In other words, some systems are 

 inducible; some are not. Thus, Bacillus megaterium 

 899[1+] ^ is inducible, as are the lysogenized strains 

 Mox[I+] and M[l + ]; on the other hand, B. megaterium 

 17 [2] and the lysogenized strains Mox[2] and M[2] are 

 not inducible. 



In the double lysogenic B. megaterium 17 [2], [1] — in- 

 ducing agents elicit the development of phage 1 only. It 

 was therefore concluded (6) that inducibility was a genetic 

 property of the prophage, a conclusion which, as will be 

 seen, is at the same time true and untrue. 



In the course of the study of B. megaterium, a defective 

 inducible strain, B. megaterium 91 [1 + ], was obtained by 

 lysogenization. The bacteria of this strain undergo lysis 

 after irradiation with ultraviolet light but do not produce 

 bacteriophage. The defective strain retained its induci- 

 bility for two years. During the third year inducibility 

 disappeared. Moreover, instead of producing the original 

 phage 1+, this strain now produced two phages, GC (G 



1 The number in brackets is the identification number of the prophage. 



