GENETIC RECOMBINATION IN BACTERIAL VIRUSES 5 



artificially broken up soon after infection, no phage will be found. 

 F^or phage T2 this period, called the "eclipse period," lasts for about 

 10 minutes. From 10 minutes to 22 minutes mature phage particles 

 can be recovered from artificially lysed bacteria. Doermann (1948) 

 has shoM-n that mature phage accumulates in the bacterium linearly 

 Mith time. 



Hershey and Chase (1952) have found that as soon as the 

 phage is adsorbed it releases its nucleic acid into the bacterial cell 

 \\hile most of the protein part of the phage remains outside stuck to 

 the bacterial surface. Only the nucleic acid part is necessary for the 

 subsequent formation of new phage. At this point we must infer a 

 mechanism by \\'hich a continuity is established between the infect- 

 ing phage particle and the progeny phage which starts appearing in 

 the bacterium 10 minutes after the infection. We assume that the 

 nucleic acid moiety of the phage forms a new entity which we call 

 vegetative phage. The vegetative phage grows in the bacterium, 

 forming a population of particles called the pool of the vegetative 

 phage. At a given moment vegetative phage particles are withdrawn 

 from this pool and transformed into mature phage particles. The proc- 

 ess of maturation which goes on linearly with time consists in the 

 phage's attainment of a protein coat formed of an external membrane 

 and a tail. When normal lysis occurs, a great many mature phage 

 particles are released and all immature particles are lost. Whereas 

 vegetative phage is the active phase of viral Hfe in the sense of growth, 

 mature phage is a dormant phase of the phage between two growth 

 cycles. 



Doermann (1951) has shown that among the first mature phage 

 particles to appear in the cell, recombinants are already present. On 

 the other hand, Levinthal and Visconti (1953) have shown that by 

 delaying the lysis, the frequency of recombinants among the liberated 

 phage particles increases considerably. 



TECHNIQUE OF PHAGE CROSSES 



The viral mutations used as markers are either host-range mu- 

 tants or plaque type mutants. The first, indicated by h, are mutants 

 which can lyse bacteria resistant to the normal h'^ phage strain. The 

 plaque mutants indicated by r differ from the normal by the morpho- 

 logical character of the plaque. 



