A. D. HERSHEY AND MARTHA CHASE 



45 



We interpret these facts to mean that intracellular DNA derived from phage 

 is not merely DNA in solution, but is part of an organized structure at all times 

 during the latent period. 



Liberation of DNA from Phage Particles by Adsorption to Bacterial Frag- 

 ments.— Tht sensitization of phage DNA to specific depolymerase by adsorp- 

 tion to bacteria might mean that adsorption is followed by the ejection of 

 the phage DNA from its protective coat. The following experiment shows that 

 this is in fact what happens when phage attaches to fragmented bacterial 

 cells. 



TABLE IV 

 Release of DNA from Phage Adsorbed to Bacterial Debris 



Phage labeled with 



S" 



pj2 



Sediment fraction 



Surviving phage 



Total isotope 



Acid-soluble isotope 



Acid-soluble after DNase. 



22 



55 



2 



29 



Supernatant fraction 



Surviving phage 



Total isotope 



Acid-soluble isotope 



Acid-soluble after DNase. 



45 

 0. 

 39 



S''- and P52-labeled T2 were mixed with identical samples of bacterial debris in adsorption 

 medium and warmed for 30 minutes at 37°C. The mixtures were then centrifuged for 15 

 minutes at 2200 G, and the sediment and supernatant fractions were analyzed separately. 

 The results are expressed as per cent of input phage or isotope. 



Bacterial debris was prepared by infecting cells in adsorption medium with 

 four particles of T2 per bacterium, and transferring the cells to salt-poor 

 broth at 37°C. The culture was aerated for 60 minutes, m/50 HCN was added, 

 and incubation continued for 30 minutes longer. At this time the yield of ex- 

 tracellular phage was 400 particles per bacterium, which remained unadsorbed 

 because of the low concentration of electrolytes. The debris from the lysed 

 cells was washed by centrifugation at 1700 G, and resuspended in adsorption 

 medium at a concentration equivalent to 3 X 10^ lysed cells per ml. It consisted 

 largely of collapsed and fragmented cell membranes. The adsorption of radio- 

 active phage to this material is described in Table IV. The following facts 

 should be noted. 



93 



