A. D. HERSHEY 



from parents to progeny involves breakdown and resynthesis of 

 DNA leaves the low efficiency of the process unexplained. 



All the evidence short of isolation and identification leads 

 to the conclusion that vegetative phage contains large amounts 

 of DNA. The possibility that DNA is its principal functional 

 component is suggested by the analysis of resting phage particles, 

 by examination of the injection mechanism, and by the com- 

 position of the material conserved during viral growth. A more 

 general confirmation of this idea has not yet proved possible but 

 promises to emerge from considerations to which we now turn. 



CORRELATION OF MATERIAL AND GENETIC CONTINUITY 



A direct correlation between the transfer of genetic markers 

 and of labeled DNA from parental to offspring virus would not 

 only answer the question about biochemical pathways but also 

 rule out the unpleasant possibility that most of the viral DNA 

 resembles more closely in function the white of an egg than it 

 does the nuclear apparatus of an ovum. Such a demonstration 

 would, in fact, reduce genetic questions about T2 to purely bio- 

 chemical questions about structure and function of DNA. Koz- 

 loff (34) recognized this very early but was unable to find any 

 correlation between genetic and biochemical results. 



Kozloff"'s basic experiment is the following. Bacteria were 

 simultaneously infected with isotopically labeled phage, pre- 

 viously exposed to ultraviolet light or x-rays, and with un- 

 labeled, unirradiated phage. Previous experiments of this type 

 with genetically marked phage had shown that the genetic 

 contribution from the irradiated phage to the mixed yield of 

 virus could be suppressed by a sufficient dose of radiation. 

 Kozloff reasoned that the contribution of isotope ought also to be 

 suppressed if the material transfer had any direct connection 

 with genetic function. Since he did not find any appreciable 

 effect of irradiation on isotope transfer, Kozloff' (34,35) concluded 

 that the material transfer from parents to progeny probably had 

 nothing to do with genetic function, and that it might very well 

 involve breakdown to nonspecific fragments en route. Watson 



18 



