REQUIREMENTS FOR PHAGE PRODUCTION 247 



Studied from this point of view, may be a case in point. Accord- 

 ing to Luria and Delbriick (1942), Tl inactivated by ultraviolet 

 light does not kill bacteria. It nevertheless produces striking 

 cytological changes in the cells (Luria and Human, 1950). In no 

 instance is it clear which effects of infection should be ascribed to 

 action localized at the cell surface and which to the injected 

 materials. Thus ultraviolet-inactivated T2 and T5 (and a few 

 other phages, perhaps) kill bacteria with high efficiency. Ghosts 

 of T2 kill with low efficiency, and adsorbed ghosts that fail to 

 kill produce transient cellular changes (French and Siminovitch, 

 1955). Systematic elucidation of these questions will be a neces- 

 sary part of the clarification of current ideas about possible 

 phage-host relationship (Stent, 1958). 



3. Partial Metabolic Requirements for Vegetative Replication 



We have just seen that multiplication of phage T2 is inde- 

 pendent of specific bacterial biosyntheses such as that of DNA, 

 certain enzymes, and probably bacterial ribonucleic acid. Even 

 more remarkable is recent evidence that synthesis of phage pro- 

 tein and DNA are to some extent independent. 



Watanabe (1957) showed that bacteria heavily irradiated with 

 ultraviolet light some time after infection with phage T2 showed 

 a markedly reduced capacity to synthesize DNA, but continued 

 to form serologically specific phage protein at an appreciable 

 rate. Their results suggest that the role of DNA in protein 

 synthesis is a passive one, as do the corresponding experiments 

 with uninfected bacteria (Kelner, 1953). 



Burton (1955) first showed that synthesis of DNA is independ- 

 ent of synthesis of protein in bacteria infected with T2. To test 

 this, he used amino acid-requiring strains of E. coli, which were 

 grown in supplemented medium, infected with phage, and 

 transferred to deficient medium at various times after infection. 

 He found that deprivation of an amino acid during the first few 

 minutes after infection could prevent phage DNA .synthesis from 

 starting, but had little eff'ect if the transfer to a deficient medium 

 was postponed until a later time. The same phenomenon was 



