262 BACTERIOPHAGES 



1954) that the pool of phage-precursor DNA is the material sub- 

 stance of which the pool of mating vegetative phage is composed. 

 The reader is referred to reviews by Hershey (1956a, 1957) for 

 additional discussion. 



In contrast with the tremendous amount of research dealing 

 with the T2 species of phage, there is a dearth of information 

 about the kinetics of assimilation of nutrients in the case of other 

 phages. Essentially all the phosphorus of phage T7 is derived 

 from preassimilated host cell phosphorus, whereas with phage Tl 

 about 70 per cent is derived from the host cells and 30 per cent 

 from the medium (Labaw, 1953; Putnam, Miller, Palm, and 

 Evans, 1952). 



Experiments with phage T5 reported by Labaw (1953) pre- 

 sent certain unique features. Labaw believes that the host con- 

 tribution to phage phosphorus is not derived from complex bac- 

 terial substances such as nucleic acids, but rather is derived 

 solely from phosphorus assimilated not over two minutes before 

 infection. The data on this point are not convincing, however, 

 and the experiments were criticized by Stent and Maal0e (1953). 

 Labaw also observed that the rapid uptake of phosphorus from 

 the medium for synthesis of phage T5 did not begin until about 9 

 minutes after infection. This may be correlated with the fact that 

 penetration of phage T5 into the host cell is a slow process, as 

 compared with T2, requiring about 10 minutes (Lanni, 1954; 

 Luria and Steiner, 1954). 



6. Summary 



The nutritional requirements for phage production have been 

 discussed from several points of view considering separately the 

 extracellular phage particle, the infected cell, and the vegetative 

 phage within the cell. It has not been possible to demonstrate 

 metabolic systems in mature phage. The phage is dependent on 

 host cell enzymes for the energy and the generalized synthetic 

 reactions required for phage reproduction although a viable host 

 cell is not required. There is some circumstantial evidence sug- 



