BIOLOGICAL ORDER 



the autonomous replication of the viral genetic material can take 

 place only if the genetic material of the phage is no longer exposed 

 to the repressor. 



1. This happens when the prophage of the lysogenic male enters 

 a nonlysogenic female where no repressor is present. 



2. This happens also if the repressor balance is upset by inducing 

 agents such as ultraviolet light. 



Let me repeat that the virulent mutants of a temperate phage are 

 unable to produce a repressor and are insensitive to the repressor 

 produced by the original prophage. They develop despite the pres- 

 ence of a repressor, and they produce the proteins necessary for the 

 onset of the vegetative phase of their own life cycle. 



It has been admitted that the prophage does not enter the vegeta- 

 tive phase because it is unable to produce some specific protein. 

 If this hypothesis corresponds to the facts, the virulent mutant, which 

 does multiply and which does produce these proteins, should induce 

 the vegetative development of the prophage. If a lysogenic bacterium 

 is infected with a virulent phage genetically related to the prophage, 

 the homologous prophage enters the vegetative phase. All the experi- 

 mental data are thus in agreement with the hypothesis that autono- 

 mous multiplication of a phage requires the manufacture of a protein. 

 The synthesis of this protein may be blocked by a specific repressor. 



Interactions of Cellular 

 and Viral Functions 



Cellular control of viral reproduction. The most important 

 aspect of the reproduction of the viral genetic material has not yet 

 been discussed. In a lysogenic bacterium, the chromosome of the 

 superinfecting bacteriophage does not multiply, whereas the pro- 

 phage multiplies, whether it is attached to the chromosome or to an 

 episome such as the sexual F factor (Figure 32). 



Thus, the behavior of two structurally identical viral chromosomes 

 might be different. Their properties seem to be controlled by their 

 position in the bacterium. Position is the fourth dimension of the 

 prophage. 



Moreover, the prophage is duplicated in harmony with the 



[80] 



