REQUIREMENTS FOR PHAGE PRODUCTION 255 



The infected cell then contains phage DNA derived from the in- 

 fecting particle and bacterial DNA derived from the degenerate 

 bacterial nuclei. Published work from various laboratories 

 (Cohen, 1947a; Kozloff and Putnam, 1950; Labaw, 1951) 

 demonstrated that phosphorus from the host cell was found in the 

 phage progeny. The utilization of host cell pyrimidines (Weed 

 and Cohen, 1951) and host cell purines (Koch, Putnam, and 

 Evans, 1952) for phage synthesis is consistent with the assump- 

 tion that the host cell DNA is available as a raw material for 

 phage production. This was proved when Kozloff (1953) re- 

 ported that host cell thymine appeared in the phage DNA, as 

 confirmed by Hershey, Garen, Fraser, and Hudis (1954). There 

 is general agreement that the conversion of host cell DNA to 

 phage DNA is more or less complete. Hershey, Garen, Fraser, 

 and Hudis (1954) obtained evidence that a small amount of the 

 host cell RNA may be utilized for synthesis of phage DNA as 

 well. The bacteria also contain large amounts of transient in- 

 termediates that contribute phosphorus to phage DNA (Hershey 

 andMelechen, 1957). 



The general conclusions about the sources of materials for the 

 synthesis of phage T2 DNA may be summarized in tabular form 

 as follows: 



As we shall see in Section 5 of this chapter, these host-cell con- 

 tributions to the substance of the phage particles are utilized 

 mainly by the first phage particles to be formed. Thus their frac- 

 tional contribution to the total yield of phage is variable depend- 

 ing on whether the yield is large or small. The efficiency of utiliza- 



