VIRAL FUNCTIONS: ORDER AND DISORDER 



the inducible one, and the noninducible one. When these strains are 

 irradiated with ultraviolet light, none of the bacteriophages develop. 

 In the presence of A ind", the phage A ind+ cannot be induced. 

 The noninductive mutation A ind" is dominant. 



When a bacterium carrying prophage A ind+ is irradiated with 

 ultraviolet light, it is induced and will produce phage (Table V). 



Table V. Variation of Inducibilitv. 



The effect of ultraviolet light can be suppressed bv superinfection 

 with the noninducible A phage. All these data are compatible with 

 the hypothesis that the noninducible bacteriophage A ind~ either 

 produces more repressor than the wild type or produces an altered 

 repressor that could, for example, be more stable. It could also 

 produce a repressor possessing a higher affinity for the hypothetical 

 operator gene of the bacteriophage. 



Mutations affecting virulence. One of the characteristics of 

 phage A is its ability to lysogenize. It is, by definition, a temperate 

 bacteriophage. Some mutations of A affect the possibility to lysogen- 

 ize (Table VI). The mutants are unable to lysogenize, but they are 

 still sensitive to the repressor, for they do not develop in a lyso- 

 genic A. It is tempting to suppose that these mutants have lost the 

 property to produce a repressor. This type of phage can finally 

 give rise to a more extreme mutant type of virulent phage. These 

 mutants are unable to lysogenize, but in contrast to their ancestor, 

 they are able to develop in a lysogenic bacterium carrying pro- 



[77] 



