298 



BACTERIAL VIRUSES. II 



been obtained to confirm the report of Taylor that T2r"'" virus contains 

 ribonucleic acid (5). It is considered possible that the method of isolating 

 virus from 5 to 6 hour lysates described above assists in the removal in the 

 low speed sediment of bacterial components containing RNA. Since pro- 

 teolysis in r+ systems is relatively weak, the prolonged period used by 

 Hook et al. (7) in the preparation of lysates may have assisted the degra- 

 dation of bacterial debris to a size which would not sediment at a low speed 

 but would at high speeds. Proteolysis in r"*" systems in F medium seems 

 even less pronounced than in broth. 



Synthesis of Virus in Labeled Host Cells — Small inocula of bacteria were 

 grown to 2 X 10* per cc. in 125 ahquots of F medium containing 0.02 to 0.05 

 millicurie of P^- in 13.7 mg. of inorganic phosphate. More than 99 per cent 



Table II 

 Radioactivity of Virus Isolated after Synthesis in P^^-Labeled Cells in Media Free of P^^ 



*Virus to cell ratio 3.0. 

 fVirus to cell ration 5.0. 



of the P of the bacteria was derived from the P of the medium. The cells 

 were washed twice with 0.85 per cent NaCl. The second washing con- 

 tained less than 0.1 per cent of the radioactivity of the original medium, as 

 determined on a Geiger-Miiller counter, kindly loaned by Dr. H. D. Brun- 

 ner of the Department of Pharmacology of the University of Pennsylvania. 



The radioactive cells were resuspended in 131 cc. of F medium containing 

 2.5 X 10~^ M tryptophan. Purified T2r+ or T4r+ virus was added and the 

 infected cultures were incubated for 5 hours and regularly assayed for virus 

 durmg this interval. The lysates were stored at 4° overnight and virus was 

 isolated as previously described. 



The DNA contents of the initial cultures, final lysates, and isolated virus 

 were determined. The radioactivity of the virus was compared with the 

 radioactivity of the miinfected host cell per unit weight of P. Samples of 

 known P content were digested in 1.2 cc. of 60 per cent perchloric acid and 

 diluted to 10 cc. after the solutions were neutrahzed to pH 4. The counting 



119 



