FATE OF INFECTING PHAGE PARTICLES 225 



phage with the protein membranes of parental phage as dis- 

 cussed previously and raises the possibility of a similar contamina- 

 tion with parental phage nucleic acid. 



Similar experimental findings were reported by French, 

 Graham, Lesley, and van Rooyen (1952) and by Watson and 

 Maal0e (1953) but their results are likewise ambiguous due to 

 the possibility of contamination of progeny particles with 

 damaged parental phage. This danger is well illustrated by the 

 following experiment of Hershey, Garen, Fraser, and Hudis 

 (1954). T2 was suspended in a 2 per cent peptone solution 

 containing P^^ When the radiation damage had reduced infec- 

 tivity to about one per cent of the initial value, the inactivated 

 phage was tested in a Blendor experiment. The damaged phage 

 adsorbed normally but injected less than 20 per cent of its 

 DNA. A mixed infection was made with P^^.i^beled, /3-ray- 

 inactivated phage and unlabeled active phage. The progeny 

 were then examined as in Kozloff's experiment but it proved im- 

 possible to interpret the results. A large proportion of the in- 

 activated phage do not inject and at the time of cellular lysis be- 

 come detached from the bacterial cells. Apparently many 

 particles killed by ionizing radiation not only fail to inject but 

 also make a weak attachment to bacteria. 



Ultraviolet radiation has less effect upon injection and here it 

 may be possible to follow the fate of the injected damaged DNA. 

 Hershey and Burgi (1956) studied this question. They repeated 

 Kozloff's experiments in which bacteria are infected with ultra- 

 violet-killed, P^Mabeled T2 and unirradiated, unlabeled T2. 

 They confirmed Kozloff's conclusion that there is normal transfer 

 of isotope from the irradiated particles to the issue of the mixed 

 infection. However, by special techniques they could show 

 that about half of the reincorporated P^^ is in noninfective par- 

 ticles among the offspring. Apparently such particles are non- 

 infective because of the radiation-damaged DNA they receive. 

 If so, the results tend to support the idea of direct transfer of large 

 pieces of DNA from parental to offspring particles — quite the 

 contrary of conclusions suggested by the early experiments of 

 this type. 



