REQUIREMENTS FOR PHAGE PRODUCTION 253 



and measured 30 to 50 per infected bacterium (assuming the 

 same sulfur content as mature phage) . By introducing S '^•'-sulfate 

 into the medium at various times during the latent period it was 

 possible to determine the time required for a newly assimilated 

 S^'' atom to appear in a mature phage particle. The average 

 elapsed time was found to be 6 to 7 minutes. These kinetic ex- 

 periments also indicated that the noninfectious S^^-containing 

 particles are actually phage precursors and not cast off waste 

 products of phage multiplication. 



More elaborate kinetic experiments in which total protein 

 synthesis and specific phage protein synthesis were determined 

 were reported by Hershey, Garen, Fraser, and Hudis (1954). In 

 confirmation of Cohen's work they found that total protein syn- 

 thesis continued at the same rate after infection as before. Syn- 

 thesis of specific phage protein began after a delay and gradually 

 accelerated until it was proceeding at about one-half the rate of 

 total protein synthesis. The nature of the remaining half of the 

 protein synthesized after phage infection is obscure but it is prob- 

 ably bacterial protein; at least much of it sediments with the 

 bacterial debris. The intriguing possibility remains that some of 

 it may be associated uniquely with vegetative phage. The ex- 

 periments suggest that there is a gradual shift from the synthesis 

 of nonphage protein to the synthesis of specific phage protein as 

 the infectious process continues. Inorganic sulfate from the 

 medium is assimilated into acid-insoluble protein in about 2 

 minutes. Early assimilated S^'' exists as phage precursor protein 

 for about 1 1 minutes before appearing in mature phage. Late 

 assimilated sulfur persists as phage-precursor for only 8 minutes. 

 The efficiency with which assimilated sulfur is converted into 

 mature phage is before infection, 5 to 10 per cent during the 

 first 5 minutes after infection, increasing to about 60 per cent 

 toward the end of phage growth. It is desirable to determine 

 the nature of the large amount of protein synthesized in phage 

 infected bacteria which never appears in mature phage. One 

 wonders if this nonphage protein is related in any way to the in- 

 fectious process. Interest in this question is heightened by the 



