VIRUS GENETICS, MULTIPLICATION, AND PHYSICS 187 



To test this, two experiments have been carried out and are here 

 described. 



Radiophosphorus Studies of Phage 



If bacteria are grown in a medium containing P^^ or S^^, and 

 then infected with bacteriophage, the resulting bursts will con- 

 tain phage which carry the radioactivity to some extent. These 

 labeled phage particles can then be used for various kinds of 

 studies of virus ])rocesses. We are here concerned with the ques- 

 tion of wliether a virus particle acts as a temj)late and stamps out 

 other particles, or operates in some other way, for example, by 

 growth and division. Some evidence, but not final evidence, can 

 be obtained from following the course of radioactivity in the 

 second generation of virus. 



If radioactive phage is used to infect a bacterium, the question 

 arises as to how much of the radioactivity is associated with a 

 hypothetical template, and how much with a part which is not 

 essential to the reproduction process. The radioactivity in the 

 latter part will presumably interchange by chemical processes 

 with the bacterial cytoi)lasm and so be removed from the phage. 

 This is indeed found to be so. If the total phage released in the 

 first generation is harvested and separated by centrifugation 

 from the bacterial debris, it is found to contain 30% of the 

 p32 originally used in the infecting i)hage (Kozloff and Putnam, 

 1950). Now it may be presumed that this P^-, which has had all 

 the nongenetic phosphorus removed from it in the first genera- 

 tion, will remain attached to the genetic part and so, if all the 

 phage is again harvested in the second generation, the same total 

 P^2 should be measured. Actually, for T-4, Maaloe and Watson 

 (1951) report that only about 30% is again recovered. Some pre- 

 liminary experiments by Forro for T-2 showed the same kind of 

 result. In view of this, it seems hard to believe that an indes- 

 tructible template, in the physical sense, is part of the multipli- 

 cation process. It is also remarkable that as high a turnover as is 

 observed takes place. It would be expected that growth and divi- 

 sion might spread the P^^ among many more virus particles, but 

 one would think that a retention of a high percentage should 

 occur. 



