PROGRESS OF THE ISOTOPIC 3IETH0D0L0GY 



1011 



Table 2. — Distkibution of ^^p qj. rpyg Bacteria between 



VIRUS P AND HOST P IN WITH Tg BACTERIOPHAGE InFECTED 



Escherichia coli 



Radioactivity of virus isolated after synthesis in ^^p.i^belled cells 



in media free of ^^P 



ing 32p^ infect them with the bacteriophage and compare the radio- 

 activity of 1 microgram of virus P and 1 mgm of host P. As seen in Table 

 2 the latter makes out 16% only of the former, proving that the bulk of 

 the virus P cannot originate from the host, it must have been taken up 

 from the medium in which it was grown. 



Host- bacterium (B) 

 4P — 



3 RNA 

 1 DNA 



Virus T2 

 (j>NO RNA 

 40% DNA 



Infecrea bacrerium 

 4P-» 



RNA 



4 DNA -*-<l 



P 



Lysis 'O-j0J^<^'^ 



Fig. 11. Shunt in phosphorus (P) utilization and nucleic acid 

 synthesis during virus multipUcation. 



We can also arrive at this result by following another procedure, i.e. 

 grow virus in unlabelled bacteria and add to the medium labelled phos- 

 phate. As seen in Table 3, the activity of 1 microgram of virus P is a 

 very high percentage of the radioactivity of 1 mgm of the phosphate P 

 added as orthophosphate to the medium. 



While the application of radioactive phosphorus permits to locate 

 the origin of the virus phosphorus that of i^C labelled glucose leads to 

 very instructive information on the origin of the ribose found in the 

 PNA and the desoxyribose found in DNA molecules. Seymour Cohn 

 demonstrated the presence in E. coli of two alternative pathways for 

 glucose metabolism as presented in Fig. 12. After the glucose being con- 



G4^ 



