The Biochemistry of the Bacterial Viruses 103 



with only a portion of the parent DNA being associated with the DNA 

 of the infected cell. With temperate phage, the bulk of the viral 

 phosphorus remains associated with the DNA of the infected cell, at 

 least during the experimental period. On the basis of the very limited 

 experimental data it seems possible that the prophage is either a nucleic 

 acid or a nucleic acid derivative, a hypothesis that is in harmony with 

 the considerable body of genetic evidence supporting the view that 

 prophage is a genelike unit located at a specific chromosomal site. 



With many prophage-containing cells, it is possible, under the col- 

 lect environmental conditions, to cause a conversion of prophage into 

 the vegetative state. However, not all prophage-containing bacterial 

 strains are capable of induction nor do all inducible strains respond 

 to the same agent. The mode of action of the inducing agents is not 

 known, and it is uncertain whether all of them behave in the same way. 

 It seems probable that their effect is on the metabolism of the lysog- 

 enized cell rather than on the prophage itself. After infection with a 

 temperate phage, one observes a delay in the division of the infected 

 cell and transient morphological changes may also occur. Eventually 

 the cells become cytologically normal again and divide regularly. 



If induction occurs, bacterial growth proceeds without bacterial divi- 

 sion during a latent period corresponding to one or two generations. 

 No phage is released (hiring this period, but if the induced lysogenic 

 bacteria are prematurely disrupted by lysozyme or cyanide, new mature 

 virus particles are found toward the end of the latent period, and 

 increase linearly until a full yield is reached. Many features of phage 

 multiplication in induced lysogenic bacteria coincide almost exactly 

 with those observed after infection of non-lysogenic bacteria with a 

 virulent phage. Such characteristics of phage development as average 

 hurst size, distribution of individual burst sizes, etc., are identical in 

 both systems with the exception of the length of the minimum latent 

 period, which is longer in induced than in infected sensitive bacteria. 



However, there are marked differences in the chemical and enzymic 

 composition of the induced bacterial cell as compared with the bac- 

 terium infected with virulent phage. After a prophage-carrying bacte- 

 rial cell has been induced, the oxygen uptake of the cell continues to 

 increase and the cell continues to grow although cell division does not 

 occur. In contrast to what is observed in the virulent process, induced 

 cells continue to synthesize RNA and are capable of forming adaptive 

 enzymes almost up to the time mature virus particles can be detected 

 in the cell. Increased synthesis of DNA and protein is a common 

 feature of both types of viral infection, although there is a delay in 



