468 ROLLIN D. HOTCHKISS 



Once lysis has been initiated by, for example, ultraviolet irradiation of 

 the host cells, net DNA synthesis is temporarily blocked, then later re- 

 sumed at an increased rate,^^* during the time that the temperate phage is 

 rapidly accumulating in the cell prior to lysis. This characteristic effect is 

 similar to that in cells synthesizing the virulent phages and indicates that 

 both kinds of phage production are accompanied by profound disturbance 

 of cell DNA metabolism. In contrast, however, the optical density increases, 

 and PNA and enzyme synthesis continue to occur almost uninterruptedly 

 up to the time of lysis in ultraviolet-induced temperate systems.^** They 

 are blocked in typical virulent phage systems as already described. 



Other viruses which have been said to contain DNA are psittaco- 

 gjg 198,199 vaccinia,^'"' rabbit papilloma,-*^^ swine influenza,-"^ and influenza 

 Pfjg 203 ^Yie last having a low content variously reported as from 0.3 to 2 % 

 DNA.^''^' 204-206 j)NA has also been found in the inclusion bodies of rabieSj^"^ 

 and neurovaccinia,^*'^ molluscum contagiosum,-"^-"^ verruca (warts) ,2"'' ■ ^<*^ 

 in various insect viruses,"^ and in Rickettsiae }^'°-^^^ It should not be for- 

 gotten, however, that some plant viruses and perhaps a few animal viruses 

 contain PNA and apparently no DNA. 



/. Transduction — A Transformation Mediated by Phage 



One of the remarkable processes brought about by certain symbiotic or 

 temperate phages, called transduction, is so analogous to transformation 

 by certain bacterial DNA's that it should briefly be mentioned here, al- 

 though there is as yet no demonstration that DNA is specifically involved. 



There were elicited from Salmonella typhimurium cells particulate prep- 

 arations able to transfer heritable traits to other strains of Salmonella}^^ 



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