FATE OF INFECTING PHAGE PARTICLES 227 



the intermediates must be nucleotides or larger fragments. 

 Kozloff (1953) summarizes early experiments in which unequal 

 transfer of parental phosphorus and DNA nitrogen was ob- 

 served. This result is inconsistent with all other comparable 

 observations, summarized by Hershey and Burgi (1956). 

 Kozloff's results remain unexplained, but it should be pointed 

 out that the transfer experiments he describes were performed 

 under conditions rather unfavorable to phage growth and ef- 

 ficient transfer. 



It must be concluded that there is no decisive evidence for or 

 against the possibility that some of the transfer occurs by way of 

 small, functionally unspecific, fragments of DNA. 



e. Distribution of Parental Isotope among Progeny Particles 



All the previous work has dealt with populations of virus 

 particles multiplying within a very large number of bacteria. 

 The measured efficiency of transfer is an average summed over 

 very many individual infections. By themselves, the incomplete 

 transfer values are compatible with the assumption that the DNA 

 of the infecting phage remains intact during replication and with 

 a certain probability becomes infective again and reappears 

 among the progeny. This possibility, however, is ruled out by 

 the P^2_suicide experiments of Hershey, Kamen, Kennedy, and 

 Gest (1951). In their experiments phage containing P^^.i^^gj^j-j 

 DNA loses infectivity upon radioactive decay (Chapter VI). 

 Uniformly P'^Mabeled bacteria growing in P^'-labeled medium 

 were infected with nonradioactive parental T4 particles. Fol- 

 lowing lysis and the release of about 100 progeny particles per 

 bacterium, the progeny were isolated and all proved to be sub- 

 ject to killing by radioactive decay. The failure to observe any 

 stable progeny indicates that none of them contained the intact 

 DNA from an unlabeled parental particle. It is clear that the 

 phage DNA does not remain in one piece but is dispersed among 

 progeny particles. 



