240 ROBERT L. SINSHEIMER 



terium carrying an inducible prophage (X) is employed as the donor in 

 a bacterial mating with a nonlysogenic recipient, the prophage will in 

 most instances be induced upon passage into the recipient cell ("zygotic 

 induction" 198 ). If the donor cells have been heavily P 32 -labeled by growth 

 in strongly radioactive media, the prophage will, if it contains phosphorus, 

 also be heavily labeled. The time of entry of the prophage into the re- 

 cipient cell is known and aliquots of zygotes can be taken at various times 

 after initiation of prophage entry — i.e., at various times during the in- 

 duction process — and then stored to permit P 32 decay. The effect of such 

 decay in the zygote upon the induction process and the ultimate produc- 

 tion of free temperate phage can then be measured. In this way, it is 

 found that the prophage apparently does contain phosphorus and can be 

 inactivated by P 32 decay. When the prophage first enters the recipient 

 cell it is inactivated at the same rate at which the free X phage of the 

 same specific P 32 activity is inactivated. This result suggests that if the 

 prophage contains DNA, it contains the same amount as the free phage, 

 assuming an equal sensitivity to P 32 decay in these dissimilar circum- 

 stances. During the zygotic induction process the sensitivity to P 32 decay 

 declines to complete insensitivity by 60 minutes after the start of the 

 bacterial conjugation. 



5. Biochemical Events Following Induction 



Following induction of a lysogenic culture (by ultraviolet irradiation) 

 RNA synthesis and protein synthesis continue and respiration increases, 

 although at decreasing rates until lysis. 185 ' 199 In the 90 minutes preceding 

 lysis at 27° (Bacillus megaterium) the RNA content and over all turbidity 

 of the culture more than double. Adaptive enzymes [e.g., 0-galactosidase 

 in K12 (X) 200 ] can be formed at any time during the latent period. These 

 observations are in distinct contrast to the parallel observations, during 

 T-even phage infection, of the cessation of RNA and host enzyme synthe- 

 sis, 99a and the loss of capacity for enzyme induction. 201 However, cell divi- 

 sion does not take place during the post-lysogenic induction period despite 

 the "residual growth." 



DNA synthesis is abruptly blocked by the ultraviolet dose employed 

 for induction. The duration of the block depends upon the temperature, 

 being less at higher temperature, and upon the ultraviolet dose employed, 

 increasing with increasing dose. At 27° a dose of 1000 ergs/sq. mm. blocks 

 DNA synthesis for 30 minutes of a 90 minute latent period (Fig. 8). 



198 F. Jacob and E. Wollman, Compt. rend. acad. set. 239, 317 (1954). 



'" L. Siminovitch and S. Rapkine, Biochim. et Biophys. Acta 9, 478 (1952). 



200 L. Siminovitch and F. Jacob, Ann. inst. Pasteur 83, 745 (1952). 



201 J. Monod and E. L. Wollman, Ann. inst. Pasteur 73, 937 (1947). 



