218 BACTERIOPHAGES 



or separated from the phage progeny and which therefore simu- 

 late a material transfer from parent to progeny. The treatment 

 of the infected bacteria in the Waring Blendor followed by cen- 

 trifugation seems to be a useful way of preventing this contami- 

 nation. These conclusions were confirmed by Kozloff (1953) 

 and by French (1954). 



Experiments by Volkin (1954a) suggested that phage T4 con- 

 tains about 30 per cent of its total protein content in tl>e form of 

 a nucleoprotein. Hershey (1955) failed to confirm this in care- 

 ful studies of phage T2 labeled with either S'''' or C^^ He did 

 find evidence for a "nonsedimentable" protein fraction in osmot- 

 ically shocked T2 preparations, amounting to about 3 per cent of 

 the total protein. This nonsedimentable protein was chemi- 

 cally similar to phage ghosts but serologically distinct and ap- 

 parently was injected into the host cell along with the phage 

 DNA. There was no evidence that this protein contributed 

 materials to the phage progeny. 



b. Transfer of Phage Nucleic Acid to Progeny 



In marked contrast to the situation with phage protein, there is 

 conclusive evidence that substances from the infecting phage con- 

 tribute to the nucleic acid of phage progeny. In experiments 

 of Hershey and Chase (1952) with P^Mabeled phage T2 there 

 was a transfer of 30 per cent of the parental phosphorus to the 

 progeny phage after treatment of the infected bacteria in the 

 Blendor. Therefore this cannot be due to residual DNA in 

 contaminating phage membranes. The results of a number of 

 other transfer experiments are recorded in Table XIV. The 

 transfer of parental nucleic acid substance to progeny varies 

 from 1 5 to 60 per cent in diff'erent experiments, the efficiency of 

 transfer depending largely on experimental conditions. The 

 percentage transfer is of the same order of magnitude for T2, T3, 

 T4, T6, and T7; for P'^^^ for DNA-N^^ and for C^^-purines and 

 pyrimidines. Much of this work has been briefly summarized 

 by Kozloff (1953), and more recent work by Hershey and 



