RECOMBINATION IN VIRUSES AND BACTERIA 147 



are located. These prophages seem to be attached to the chromosome in 

 a different way than are the inducible prophages. To demonstrate this, 

 the fact was used that the decay of P'^^ in the genetic material of a bac- 

 terium destroys its ability to reproduce. If a prophage were in some way 

 independent of the bacterial chromosome, P^^ decay should kill it inde- 

 pendently of the host. As a result, the suryivors of such decay should 

 include some nonlysogenic cells. But if the prophage were inserted in 

 and acted as an integral part of the bacterial chromosome, a disintegra- 

 tion lethal for the prophage might also be lethal for the host. The 

 failure in such experiments to recoyer bacteria that are free of the non- 

 inducible prophages implies that they are inserted, at least to a consider- 

 able extent. On the other hand, the inducible prophages are easily lost 

 by this method, suggesting that they may be inserted at a chromosomal 

 locus at the most to a limited extent. 



Another test of the continuity of the inducible prophage of X is had in 

 experiments in which exchanges between prophage genes are obseryed in 

 a bacterial cross. Figure 5.18 shows how, if the prophages were in- 

 serted in bacterial chromosome, such exchanges would be expected 

 to recombine outside markers, except where multiple exchanges occur in 

 the prophage. The results are not in agreement with the insertion 

 hypothesis. The prophage appears to be an entity, at least a part of 

 which is an addition to the bacterial genotype. There does not seem to 

 be in nonlysogenic bacteria an allele alternatiye to the whole of the 



TABLE 5.9 



The Location of a Variety of Inducible Prophages 



in the gal Region of the E. co/i Chromosome 



(From Jacob and Wollman, 1957, in McElroy and Glass, 

 The Chemical Basis of Heredity. Baltimore: The Johns Hopkins Press, p. 468) 



lac galb 82 X 434 381 21 424 466 



A is the per cent of galh^ ly~ str-r recombinants from crosses of Hfr galy' 

 ly~ str-s X F~ galh~ ly^ str-r." 



B is the per cent of input Hfr whose mating results in zygotic induction in 

 crosses of Hfr ly^ str-s x F~ ly~ str-r. 



C is the time at which the prophage enters the F~ cell when the parents are 

 mixed at time 0. 



° ly stands for the Ivsogenic and /;/" for the nonlvsogenic condition. 



