378 F. W. STAHL 



C. Luria-Latarjet Experiments 



In these experiments, cells infected singly with, radioactive phage are 

 allowed to incubate for various lengths of time before their development is 

 suspended by freezing. With T2, the survival curves obtained by periodic 

 assay of these frozen samples are highly reminiscent of the curves obtained 

 with ultraviolet light. For the first 5 to 6 minutes there is very little (Stent, 

 1955) or no (Symonds and McCloy, 1958) change in sensitivity of the com- 

 plexes. Thereafter, there is a rapid rise of resistance, so that by about 9 

 minutes the complexes are apparently totally resistant to the decay of 

 phosphorus in the infecting particle. 



The obvious interpretation of this experiment is that by 9 minutes there 

 is in every cell at least one new, nonradioactive copy of the infecting phage. 

 This would insure phage production by these cells independently of the in- 

 activation of the original, radioactive, infecting particle (Stent, 1953b). 

 This simple interpretation was simply ruled out by a repeat of the same 

 experiment using radioactive bacteria growing in radioactive medium (Stent, 

 1955). The complexes stabilized in essentially the same fashion. Stent (1955) 

 suggested three interpretations of this result: (1) Phage DNA in the cells at 

 9 minutes is in a P^^.p^sistant state. (2) The genetic information of the 

 infecting particle has been transferred to a P^^.j-^gigtant structure. (3) Multi- 

 plicity reactivation at 9 mmutes is highly efficient. The following experiment 

 (Steinberg, personal communication) suggests that multipHcity reactivation, 

 although not demonstrable for phages which are allowed to decay at an 

 early stage in development, might indeed be efficient for phages inactivated 

 after 9 minutes of development. 



Steinberg infected K12(A) with radioactive wild-type T4 at a low (ca. 0.1 

 particles per cell) multiplicity and with about 1 per cell of a T4rII mutant 

 which was not radioactive. The infected cells were allowed to develop for 

 various lengths of time before they were frozen. Survival curves for the 

 function of the rll cistron were then obtained by assaying at intervals for 

 the ability of the cells to yield phage. Innnediately following infection, the 

 function of the rll cistron was about one-third as sensitive as the whole 

 phage. By 6 minutes, however, the function had become so resistant that 

 no inactivation was detected. This finding suggests that whereas multipli- 

 city reactivation might be inefficient in very early complexes because of 

 the extreme sensitivity of the function of cistrons required for duphcation, 

 it might be thoroughly efficient after 6 minutes, by which time these functions 

 have been performed. 



At present it seems that the Luria-Latarjet experiments with suicided 

 phage may well have an explanation essentially identical to that proposed 

 for ultraviolet-irradiated complexes. In this regard, it would be helpfid to know 

 the effect of P^^ decay on genetic recombination in stable, 9-minute complexes. 



