BACTERIOPHAGE GENETICS 333 



types found in the yields. These methods were described by 

 Hershey and Rotman (1948, 1949). 



2. The Vegetative Phage Pool 



Following adsorption of a phage T2 particle to the host cell 

 surface, the phage nucleic acid but not the protein penetrates 

 through the cell wall into the cell interior (Hershey and Chase, 

 1952). After a lag of a few minutes, copies of the phage DNA 

 begin to be synthesized and this DNA forms a pool of 50 to 1 00 

 phage equivalents of DNA per infected cell by 1 minutes after 

 infection. At this time phage DNA begins to be withdrawn from 

 the pool and is coated with protein to form mature phage par- 

 ticles. From this time on new phage DNA is synthesized and 

 added to the pool at the sam.e rate that DNA is withdrawn from 

 the pool by the process of phage maturation so that the pool size 

 remains constant. These processes of DNA synthesis and phage 

 maturation continue until interrupted by host cell lysis. Once 

 phage DNA has been incorporated into a mature phage particle 

 it is isolated biochemically from the DNA pool; maturation 

 is irreversible. Over a considerable period of time the rate of 

 DNA synthesis and of phage maturation is constant presumably 

 because a constant amount of synthetic machinery is function- 

 ing at capacity (Hershey, 1 953a) . 



The work of Luria (1951) on the frequency distribution of 

 mutant phage particles in single cell bursts demonstrated clearly 

 a clonal rather than a Poisson distribution with an exponential 

 distribution of clone sizes. This result indicates that each new 

 vegetative phage particle can serve as a pattern for the synthesis 

 of daughter phage particles. This replication of patterns may 

 be interrupted by maturation which withdraws one copy of the 

 pattern for each mature phage. If there is only one copy avail- 

 able at the time it is included in a mature phage particle, the 

 clone size will be one in that bacterium. Maturation results in 

 genetic as well as biochemical isolation. 



If a susceptible bacterium is infected simultaneously with 

 two genetically distinguishable phage particles such as Tlh'^r 



