52 VIRAL PROTEIN AND NUCLEIC ACID ]N BACTERIOPHAGE GROWTH 



except that a small amount of the contaminant could be removed by adsorp- 

 tion to bacteria resistant to the phage. In addition to the properties already- 

 mentioned, the contaminating S^* is completely precipitated with the phage 

 by antiserum, and cannot be appreciably separated from the phage by further 

 fractional sedimentation, at either high or low concentrations of electrolyte. 

 On the other hand, the chemical contamination from this source would be 

 very small in favorable circumstances, because the progeny of a single phage 

 particle are numerous and the contaminant is evidently derived from the 

 parents. 



The properties of the S^Mabeled contaminant show that it consists of the 

 remains of the coats of the parental phage particles, presumably identical 

 with the material that can be removed from unlysed cells in the Waring blen- 

 dor. The fact that it undergoes little chemical change is not surprising since it 

 probably never enters the infected cell. 



The properties described explain a mistaken preliminary report (Hershey 

 et al., 1951) of the transfer of S^^ from parental to progeny phage. 



It should be added that experiments identical to those shown in Tables VI 

 and VII, but starting from phage labeled with P^-, show that phosphorus is 

 transferred from parental to progeny phage to the extent of 30 per cent at 

 yields of about 30 phage per infected bacterium, and that the P^- in prema- 

 turely lysed cultures is almost entirely non-sedimentable, becoming, in fact, 

 acid-soluble on aging. 



Similar measures of the transfer of P^'^ have been published by Putnam and 

 Kozlofif (1950) and others. Watson and Maaljzie (1952) summarize this work, 

 and report equal transfer (nearly 50 per cent) of phosphorus and adenine. 



A Progeny of S^^-Labeled Phage Nearly Free from the Parental Label. — -The 

 following experiment shows clearly that the obligatory transfer of parental 

 sulfur to offspring phage is less than 1 per cent, and probably considerably 

 less. In this experiment, the phage yield from infected bacteria from which 

 the S^Mabeled phage coats had been stripped in the Waring blendor was 

 assayed directly for S^^. 



Sensitive bacteria grown in broth were infected with five particles of S^^-Iabeled 

 phage per bacterium, the high ratio of infection being necessary for purposes of as- 

 say. The infected bacteria were freed from unadsorbed phage and suspended in water 

 containing per liter 1 mM MgS04, 0.1 mM CaCl2, and 0.1 gm. gelatin. A sample of 

 this suspension was agitated for 2.5 minutes in the Waring blendor, and centrifuged 

 to remove the extracellular S^\ A second sample not run in the blendor was centri- 

 fuged at the same time. The cells from both samples were resuspended in warm 

 salt-poor broth at a concentration of 10^ bacteria per ml., and aerated for 80 min- 

 utes. The cultures were then lysed by the addition of 0.02 mM HCN, 2 X 10" UV- 

 killed T2, and 6 mg. NaCl per ml. of culture. The addition of salt at this point causes 

 S^^ that would otherwise be eluted (Hershey et al., 1951) to remain attached to the 



100 



