FATE OF INFECTING PHAGE PARTICLES 209 



consist almost exclusively of a sulfur-containing protein mem- 

 brane and a DNA core, which can be separated from each other 

 by osmotic shock. The membrane is undamaged by this pro- 

 cedure as far as can be observed in the electron microscope and 

 retains important physiological properties (Chapter V). 



c. Physiological Fractionation — the Blendor Experiment 



Phage T2, difTerentially labeled with S^'^ and P^', is adsorbed 

 to the host cells in a salt medium which insures a high efficiency 

 of attachment. The infected bacteria are freed of unadsorbed 

 isotopic material by centrifugation and resuspension in an appro- 

 priate diluent. The infected bacteria are now vigorously agi- 

 tated in a Waring Blendor, centrifuged, and both bacteria and 

 supernatant fluid assayed for S^^ and P^^. The stirring in the 

 Blendor has essentially no effect on the plaque-forming potential 

 of the infected bacteria. After this treatment about 80 per cent 

 of the phage S^^ is found in the supernatant in the form of protein 

 which is sedimentable after two hours at 12,000 X g and is 

 precipitable by anti-T2 serum. From 20 to 35 per cent of the 

 phage P^2 is left in the supernatant, the rest being sedimented 

 with the bacteria. This means that 80 per cent of the phage pro- 

 tein can be separated from 65 to 80 per cent of the phage DNA 

 phosphorus by the physiological procedure of infection of the 

 host cells. The Blendor serves to tear the phage membranes 

 loose from the bacterial surface, but the separation of phage DNA 

 from phage protein has already occurred as a stage of infection. 



d. Functional Differentiation of Phage Protein and Phage DNA 



These experiments demonstrate that at least 80 per cent of the 

 sulfur-containing proteins of the phage remain on the surface of 

 the infected bacteria, from which they can be detached by agita- 

 tion in the Blendor. Because this treatment has no efTect on the 

 course of the infection, it may be concluded that the bulk of the 

 phage protein is expendable after infection and plays no role in 

 the intracellular multiplication of phage. Similar conclusions 



