ACTIVE FROM INACTIVATED BACTERIOPHAGE 121 



bacteria immediately after infection are similar to the curves for the probabil- 

 ity of reactivation for a comparable group of irradiated particles. For example, 

 the suppression curve given by Luria and Latarjet (1947) for bacteria 

 infected by five particles of phage T2 is very similar to the curve for the prob- 

 ability of reactivation w as a function of r for x = 5. It is clear that in interpret- 

 ing experiments on inactivation of intracellular phage it will be necessary to 

 take into account the occurrence of genetic transfers.* 



SUMMARY 



Coli-bacteriophages TZ, T4, T5, and T6 inactivated by ultraviolet light 

 are still adsorbed by sensitive bacteria. Bacteria infected by only one inactive 

 phage particle are not lysed and do not yield active phage. Infection of bacteria 

 with more than one inactive particle leads to lysis and production of active 

 phage in a fraction of the bacteiia. This fraction diminishes with increasing 

 doses of radiation and increases with increasing numbers of particles adsorbed 

 per bacterium. The assumption is made that inactivation is due to lethal 

 mutations in a number of genetic "units" of the phage particle, and that pro- 

 duction of active phage from inactive is due to recombination of non-lethal 

 units to form active particles. The values of the probability of active phage 

 production calculated from these assumptions agree with the experimental 

 results with certain limitations. In order to explain the very high frequency 

 of recombination, the hypothesis is proposed that phage growth occurs by 

 independent reproduction of each unit followed by reassembly of the units into 

 complete phage particles. The minimum number of units per particle is esti- 

 mated for various phages. 



LITERATURE CITED 



Bland, J. O. W., and C. F. Robinow, 1939 The inclusion bodies of vaccinia and their relation- 

 ship to the elementary bodies studied in cultures of the rabbit's cornea. J. Path. Bact. 48: 

 381-403 



Cohen, S. S., 1948 The synthesis of bacterial viruses. I. The synthesis of nucleic acid and protein 

 in Escherichia coli B infected with T2r^ bacteriophage. J. Biol. Chem. 174: 281-293. 



DelbrOck, M., 1940 The growth of bacteriophage and lysis of the host. J. Gen. Physiol. 23: 

 643-660. 

 1946 Bacterial viruses or bacteriophages. Biol. Rev. Cambridge Phil. Soc. 21 : 30-40. 



Delbruck, M., and W. T. Bailey, Jr., 1946 Induced mutations in bacterial viruses. Cold 

 Spring Harbor Symp. Quant. Biol. 11: 33-37. 



DELBRticK, M., and S. E. Luria, 1942 Interference between bacterial viruses. I. Interference 

 between two bacterial viruses acting upon the same host, and the mechanism of virus growth. 

 Arch. Biochem. 1: 111-141. 



DoERMANN, A. H., 1948 Intracellular growth of bacteriophage. Carnegie Instn. Wash. Yearb. 

 (in press). 



^ While this paper was in press, one of us (Dulbecco 1949b) discovered that ultraviolet ir- 

 radiated phages can be reactivated by exposure to visible light of short wave length in presence 

 of bacterial cells. This "photoreactivation" differs from reactivation by multiple infection in many 

 of its features. Photoreactivation does not take place to any appreciable extent under the condi- 

 tions in which the experiments reported in this paper were performed. A series of experiments of 

 the type exemplified in table 4, but carried out in dim yellow light — ^under conditions that com- 

 pletely avoid photoreactivation — gave results undistinguishable from those of the earlier experi- 

 ments, in which no precaution had been taken to control illumination. 



275 



