FATE OF INFECTING PHAGE PARTICLES 211 



could be liberated from the infected bacteria by violent agitation, 

 together with about 80 per cent of the carbon of other amino acids 

 (Hershey, 1955). All of the liberated S^^ is sedimentable at high 

 speed and specifically precipitable by antiphage serum, which in- 

 dicates that the fragments must be more or less intact phage mem- 

 branes. Examination of the liberated phage membranes in the 

 electron microscope shows them to have damaged tails, suggesting 

 that part of the missing 20 per cent of phage S'^ may consist of 

 phage tail tips which remain fixed to the bacterial surface when 

 the remainder of the phage is torn away in the Blendor. Much 

 of the residual S^^ remains attached to the bacterial debris after 

 bacterial lysis and when the final phage lysate is analyzed only 

 about 2 per cent of the initial phage S^^ is found in the superna- 

 tant after centrifugation at 12,000 X g for 30 minutes (Hershey 

 and Chase, 1952). These experiments indicate that essentially 

 none of the proteins of the infecting T2 phage are converted into 

 low molecular weight fragments during the infectious process. 

 This is in agreement with the basic assumption that once the in- 

 jection of phage DNA into the host cell has been completed the 

 phage protein plays no further role in the infectious process, but 

 remains physiologically inert, outside of the bacterial cell wall. 

 Experiments by French (1954) are in essential agreement with 

 these conclusions. French prepared stocks of phage T2 which 

 were labeled with 2-G^^ lysine. He was able to demonstrate by 

 fractionation procedures that in the purified phage more than 

 90 per cent of the C^'^ label was in the lysine of the phage protein. 

 This labeled phage was then used to infect host bacteria at a 

 multiplicity of 10 and after lysis the lysate was fractionated by 

 centrifugation and the distribution of the C^^ label was deter- 

 mined. The bacterial debris, sedimented at 5000 X g, con- 

 tained 83 per cent of the C^^, and the high speed supernatant con- 

 tained 1 1 per cent. Unfortunately this nonsedimentable mate- 

 rial was not further investigated so it is not known whether it con- 

 sisted of phage protein or of smaller brciikdown products. Only 

 1.2 per cent of the label was found in the final yield of purified 

 phage. One may conclude from these experiments that there is 



