26 



MOLECULES, VmUSES, AND BACTERIA 



Osmotically shocked ghosts of T-even phages, although capable 

 of adsorbing to the bacteria and aflFecting bacterial metabolism, 

 cannot induce enzyme. The contents of the phage head are 

 therefore essential for the appearance of enzyme. These con- 

 tents consist mainly of DNA and small amounts of a specific 

 internal protein (Levine et al., 1958), a polypeptide (Hershey, 

 1957), and polyamines (Ames et al., 1958). The polyamines 

 may be replaced by other cations in the phage without affecting 

 phage viability (Ames and Dubin, 1960). 



The contents of the phage head do not contain free pyrimidine 

 deoxyribonucleotides (Flaks et al., 1959), which might be im- 

 agined to induce the biosynthesis of the hydroxymethylase. 

 As presented in Figure 4, ultraviolet-irradiated phages induce 

 the appearance of the enzyme in normal amount under condi- 

 tions (15 hits, virus: cell ^ 4) in which virus cannot multiply* 

 nor induce the formation of DNA (Flaks et al., 1959). This work 

 has been extended to a study of single infection with irradiated 

 phage using the column assay. It appears that the site in the 

 phage that controls the appearance of enzyme has a sensitivity 

 to ultraviolet light about 1/20 that of all the sites that control 



10 20 30 40 50 60 

 UV IRRADIATION (SECONDS) 



Figure 4. The effect of ultra- 

 violet irradiation of virus on 

 hydroxymethylase formation. 

 Cells were multiply infected 

 with virus irradiated to vary- 

 ing levels of survival. The en- 

 zyme contents of such in- 

 fected cells were determined. 



* E. coU strain W will adsorb T2 and be killed by this phage without giving 

 rise to DNA and virus (Fowler, unpublished results; Cohen, 1953). Despite the 

 abortive quality of the infection, this strain will produce dCMP hydroxymethylase 

 ( Pizer and Cohen, unpubhshed results ) . 



