126 Information Storage and Neural Control 



In either case, the DNA of the cell is not destroyed. In the cell 

 undergoing the lysogenic response about a two-hour lag occurs 

 after infection before the cell resumes growth (23). The phage 

 genome has by this time become attached to the bacterial chromo- 

 some where it is carried in the form of prophage as a new genetic 

 character of the cell. According to current belief, phage genes in 

 a lysogenic cell do not function because a repressor is formed by 

 one phage gene which prevents the expression of the others (24). 

 Certain mutations (virulent) among temperate phages result in a 

 change in character of the phage so that it no longer can lysogenize 

 cells but can only lyse them. The mutation is presumably due to 

 a loss of the repressor. A strong piece of evidence in support of 

 this hypothesis is that separately arising, virulent mutants can 

 complement each other during mixed infections to produce 

 lysogenization (25, 26). 



The basis for the profound difference in effect on the bacterial 

 chromosome between temperate and intemperate phages is ill 

 understood at present, but may be related in some way to the 

 close relationship between phage DNA and host DNA in the case 

 of the temperate phages. For instance, base ratios between tem- 

 perate phages and their hosts are similar (27). In addition, the 

 capacity of a bacterial cell to support multiplication of a temperate 

 phage is much more sensitive to inactivation by physical agents 

 which damage the nucleic acids than in the capacity to form lytic 

 phages (28). Also, unirradiated host cells are able to repair damage 

 to irradiated temperate phages, permitting growth of the phage. 

 It is therefore clear that during the replication of temperate phages 

 there is very close interrelationship between intact functioning 

 cellular DNA and phage DNA. It is widely presumed that this 

 affords opportunity for the attachment of the phage DNA to the 

 chromosome of the cell and for the establishment of lysogeny. 



ANIMAL VIRUSES: EFFECT ON CELLULAR SYNTHESIS 



With this brief summary of the possible interrelationships be- 

 tween bacteriophages and their hosts in mind, we will now discuss 

 the impact of viral infection on the synthetic processes in animal 

 cells. In the past ten years, techniques for the study of many 



