The Biochemistry of the Bacterial Viruses 99 



decreases. At a time approximately half the period between infection 

 and lysis, disruption of the cell shows that mature infectious virus 

 particles are beginning to appear. However, viral DNA continues to 

 increase, and remains in excess of that present as infective particles, 

 until the cell finally lyses. 



The mature virus particle may contain material derived from (a) 

 the parent infecting particle, (b) the bacterial host cell, and (c) the 

 nutrient components of the medium. We have already seen that appar- 

 ently the only contribution of the parental particle is its nucleic acid. 

 By the use of isotopes it is possible to show that, although components 

 of the parental DNA appear in the viral progeny, they are confined 

 to the particles synthesized in the earlier stages of the infectious 

 process, i.e., by the time 25$ of the virus yield is completed, most 

 of the parental DNA has been transferred, and the virus particles 

 synthesized subsequently contain little or no parental nucleic acid. 

 Further, the phosphorus transferred is not localized in specific or spe- 

 cially conserved parts of the nucleic acid of the first progeny, but is 

 uniformly distributed in each particle. Experiments with parent virus 

 labeled with both N 15 and P 32 confirm the view that extensive re- 

 arrangement of the transferred material occurs. Up to now no positive 

 correlation has been obtained between the material transfer of DNA 

 from the infecting phage and the transfer of hereditary units, although 

 parental DNA must be the agent whereby these units are transmitted. 

 If special parts of the virus are conserved and transferred to the 

 progeny as nucleic acids of considerable size and possessing genetic 

 specificity, no experiment has yet revealed their existence. Rather, it 

 appears that, after that portion of the viral DNA which is effective 

 in the synthesis of new virus particles has exerted its effect on the 

 metabolism of the host cell, it is broken down into smaller fragments 

 which are then used for virus synthesis in a non-specific manner. 



The most striking feature of the utilization of the components of the 

 host cell for virus synthesis is the use of practically all of the bacterial 

 DNA. This first involves breakdown of the bacterial nucleic acid into 

 smaller fragments which are then used for the synthesis of viral DNA, 

 and especially for the viral particles which are formed in the early 

 stages of the infectious process. To the extent that there is sufficient 

 bacterial DNA to account for the whole of the DNA of the viral prog- 

 eny, relatively little synthesis of viral DNA from the components 

 of the medium takes place. However, when bacterial DNA is insuf- 

 ficient in amount for the DNA of the viral progeny, or when viral 

 DNA requires the synthesis of a qualitatively new component such as 



