CHEMISTRY AND VIRAL GROWTH 



The amount of DNA in an uninfected bacterium growing in 

 glucose-ammonia medium averages about 40 phage equivalents 

 (8 X 10~^ 7). After infection, viral precursor DNA is synthe- 

 sized at the rate of about three phage equivalents per bacterium 

 per minute and accumulates to roughly 40 equivalents per 

 bacterium. The amount of bacterial phosphorus (assimilated 

 before infection) that is used to make viral DNA measures about 

 40 phage equivalents. The total amount of preassimilated RNA 

 phosphorus per bacterium is nearly 400 phage equivalents. 



If 5 per cent of the total RNA were undergoing moderately 

 rapid turnover, E.NA synthesis could easily keep pace with DNA 

 synthesis, without having been detected in the experiments cited 

 above. It has been suggested that this happens (22). 



If 10 per cent of the total preassimilated RNA were con- 

 verted into viral DNA, this source would account for an ap- 

 preciable part of the observed use of preassimilated materials by 

 the virus, and would not readily be detected as a significant 

 decrease in RNA content of the culture. As a matter of fact, 

 one does observe a significant decrease in acid-insoluble RNA 

 when measured in terms of preassimilated isotope, and indirect 

 evidence suggests that some of the purine and pyrimidine carbon 

 enters DNA (29). 



These remarks are intended to show that an active role of 

 RNA in the growth of T2 has not been entirely excluded. Since 

 the T2-infected bacterium is the only known biological system in 

 which synthesis of RNA during growth may not occur, more 

 penetrating experiments designed to test this possibility are 

 called for. 



MATERIALS CONSERVED DURING REPRODUCTION 



A special method of defining the composition of vegetative 

 phage — perhaps a minimum composition, perhaps an irrelevant 

 one — consists in tracing those structures that pass intact from 

 parental to offspring phage. It is now generally agreed that 

 only the constituents of the parental DNA are transferred (17, 



15 



