248 BACTERIOPHAGES 



discovered independently by Tomizawa and Sunakawa (1956), 

 who used the antibiotic chloramphenicol to inhibit protein syn- 

 thesis (Wisseman, Smadel, Hahn, and Hopps, 1954). 



Hershey and Melechen (1957) made a thorough study of the 

 action of chloramphenicol in T2-infected bacteria. Suitable 

 time schedules of chloramphenicol inhibition and reversal, to- 

 gether with labeling of phage precursors by means of radioactive 

 isotopes, showed that large amounts of typical phage precursor 

 DNA could be accumulated in cells that contained virtually no 

 phage precursor protein. When such cells were transferred to a 

 medium free from chloramphenicol, phage particles were formed 

 that contained principally the phosphorus of DNA formed be- 

 fore, and protein formed after, the removal of the antibiotic. 

 These findings constitute the chief evidence for the view (Her- 

 shey, 1953b) expressed frequently in this book, that vegetative 

 reproduction and maturation in phage T2 can be equated, re- 

 spectively, with synthesis of phage DNA and protein. According 

 to Hershey (1957) the evidence is still incomplete. 



Another line of evidence pointing in the same direction may 

 be cited here. Watanabe, Stent, and Schachman (1954) in- 

 fected bacteria with P^^-labeled particles of phage T2 and subse- 

 quently broke open the infected cells and measured the sedimen- 

 tation constant of the P^Mabeled DNA in the extracts. Depend- 

 ing on the time of breakage of the cells, the labeled material 

 sedimented like free DNA or like mature phage particles. No 

 evidence was found for phosphorus-containing structures of 

 intermediate complexity. The authors interpreted their results 

 to mean that phage precursor DNA does not form stable attach- 

 ments to complex particles in the cell until incorporated into a 

 finished phage particle. 



4. Sources of Material for Phage Synthesis 



Three sources of the raw inaterials used for the formation of 

 phage particles can be distinguished by the appropriate use of 

 isotopic tracers: the substance of the parental phage particles, 

 the bacterial contents at the time of infection, and the culture 



