224 BACTERIOPHAGES 



little of the phosphorus of T2 phage is incorporated into Tl or 

 T7 progeny." 



A definitive experiment involving heterologous transfer of 

 phage label was reported by Watson and Maal0e (1953). Bac- 

 teria were mixedly infected with 5 particles of unlabeled T4r 

 and 1 particle of P*--labeled T3 per bacterium. Under condi- 

 tions of simultaneous infection with this pair of phages, T3 is ex- 

 cluded from multiplication in essentially all bacteria. In one 

 such experiment 24 per cent of the P^^ label was in the bacterial 

 debris, 49 per cent was not sedimentable, and 27 per cent was in 

 the purified phage yield. Of the P"*'- in the phage yield only 4 

 per cent was precipitated by anti-T3 serum, whereas 92 per cent 

 was precipitated by anti-T4 serum. The authors concluded that 

 about 25 per cent of the P^^ label of the excluded T3 phage was 

 incorporated into the yield of T4. This experiment seems to 

 demonstrate quite conclusively that material transfer can take 

 place between unrelated phages in the absence of genetic transfer 

 and under conditions in which the donor phage does not multiply. 

 The reasonable assumption is that the excluded donor phage 

 was extensively degraded inside the host cell and part of its 

 chemical substance used as raw material for multiplication of the 

 dominant phage. In different experiments, V2 to Vs of the P'^^ of 

 the excluded phage was liberated on host cell lysis in a form not 

 sedimentable at 12,000 X g, further evidence that extensive 

 degradation of the excluded phage occurs. 



2. Material transfer from inactivated phages. In the experiments 

 of KozlofT (1952b), N^Mabeled T6 was inactivated with various 

 doses of ultraviolet light or X-rays, mixed with unlabeled active 

 T6, and the mixture used to infect bacteria. The T6 progeny 

 was isolated and the amount of label incorporated into progeny 

 nucleic acid and protein determined. Between 5 and 18 per 

 cent of the parental N^'' was found in the nucleic acid of the 

 phage yield and Kozloff^ concluded that transfer had occurred. 

 This interpretation, however, is weakened by the parallel finding 

 that from 4 to 15 per cent of the parental N^^ was found in 

 progeny protein. This is evidence for contamination of progeny 



