440 



J. D. WATSON, O. MAAL0E VOL. 10 (1953) 



TABLE VIII 



TRANSFER OF '^P FROM EXCLUDED PHAGE 



Bacteria were mixedly infected with an average of 5 particles of T4r and i particle of labelled 

 T3 per bacterium. Following lysis the progeny particles were isolated and tested for radioactivity. 



DISCUSSION 



We shall now discuss the results of the seven different types of experiments de- 

 scribed in the preceding section in relation to the problem of virus reproduction. First 

 it must be stressed, however, that in all our experiments only the nucleic acid portion 

 of the phage has been labelled ; entirely different results are obtained if a specific protein 

 labeUing isotope, like ^^S, is used, (Hershey and Chase^^). 



1. Infection of unlabelled bacteria with ^sp-labelled T4r phage results in the transfer 

 of 40 to 50% of the label to the progeny particles. The transmitted phosphorus is truly 

 incorporated into the new phage. When the infected bacteria lyse, 5 to 10% of the 

 parental ^^p remain associated with the bacterial debris; this may mean that 5 to 10% 

 of the adsorbing particles stay passively attached to the bacterial surfaces. In our 

 experiments the transfer value is an extremely reproducible figure and must be close 

 to the maximum value since (a) nearly all the adsorbed particles participate in the 

 reproduction process, and (b) all the progeny particles are recovered. The transfer value 

 is constant for different preparations of labelled phage. 



2. For maximum ^ap transfer to occur, all the phage particles which adsorb on a 

 bacterium must do so within about two minutes. Particles which adsorb more than 

 two minutes after the primary infection of the cell do not transfer significant amounts 

 of 32p. Half the ^^p of such late adsorbing particles remains attached to the bacterial 

 debris; the rest appears within a few minutes in the medium as material soluble in 5% 

 trichloroacetic acid. In contrast, over 95% of the ^^p of the early adsorbing phage is 

 retained in the infected cells until lysis. Under conditions of almost simultaneous 

 infection, the transfer value per infecting particle is constant for multipHcities of infection 

 up to ten. 



3. 32p-iabelled T2 phage shows the same transfer as T4, and, according to Putnam 

 AND KozLOFpi and Kozloff^, similar maximum values are obtained with the related 

 phage T6. The unrelated phage T3 transfers about 40% of its phosphorus to the progeny. 

 Thus an incomplete ^^P transfer of 40 to 50% may be a general characteristic of phage 

 reproduction in E. coli. 



4. If the purines of T2, T3 and T4 phages are labelled with i*C, transfer values are 

 obtained which do not differ from those obtained with ^^P. This suggests that the purine 

 bases and the phosphorus are not transferred independently but as the constituents 

 of nucleotides or larger units. 



References p. 442. 



113 



