The Biochemistry of the Bacterial Viruses 101 



ponents of the mature 1 particle are made independently and arc assem- 

 bled only at a terminal stage of the replication process. 



Consideration of the temperate viruses and of the lysogenic relation- 

 ship between virus and host discloses much less chemical and bio- 

 chemical data than is available with their virulent analogs. Little 

 is known about the chemistry of the temperate viruses. Large-scale 

 preparations of the temperate virus A which lysogenizes the E. coll 

 strain K 1L . have been made in several laboratories. These preparations 

 appear homogeneous under the electron microscope and consist of tailed 

 particles similar in size and appearance to those of Ti. They contain 

 roughly oO'yr DNA and are free of 5-HMC (see Table 1 for purine 

 and pyridine composition I . Preparations of A show a tendency towards 

 spontaneous inactivation and are difficult to assay; little has been 

 done with respect to their detailed physicochemical characterization. 



When a bacterial cell is exposed to a temperate phage, a variety oi 

 interactions may take place. The bacteria may be non-responsive and 

 remain entirely uninfected. Or. infection may occur but the phage 

 disappears in an unknown fashion, i.e., the infection is said to have 

 been aborted, and, although the bacterial cell may die, viral repro- 

 duction does not occur. Under other circumstances, phage may be 

 reproduced with lysis of the bacterium, i.e., the phage behaves as a 

 virulent virus, and the situation is comparable to that described earlier. 

 In the case we are most concerned with, the temperate phage is 

 adsorbed and the bacterium survives to give rise to what is known 

 as a lysogenic clone. The infecting virus particle is transformed (re- 

 duced I into what is termed a prophage, and the host cell continues 

 to grow and reproduce in a normal fashion. In growing cultures of 

 such cells, one finds that in a very small proportion of the cells the 

 prophage passes spontaneously into what is known as a vegetative 

 phase and mature phage particles are then produced. This results 

 in the lysis of the particular cells concerned, with the liberation into 

 the medium of phage particles identical with the original parent. This 

 occurs spontaneously, to a small extent, and for unknown reasons. 

 However, in the case of certain lysogenic strains, it is possible to cause 

 a practically complete conversion of the prophage by treating the 

 lysogenic cells with one of a variety of so-called inducing agents. 

 These include ultraviolet light, soft X rays, y rays or radioactive cobalt, 

 thiomalic acid, reduced glutathione, ascorbic acid, organic peroxides. 

 epoxides, ethylene imines, nitrogen mustards, and hydrogen peroxide 

 either added directly or produced by the addition of sulfhydryl com- 

 pounds in the presence of copper. When such substances are applied 



