258 BACTERIOPHAGES 



Experiments by Maal0e and Stent (1952) indicated that dur- 

 ing phage maturation there was no stage in which immature 

 phage particles containing DNA could be detected by centrifuga- 

 tion, by precipitation with antiphage serum, or by adsorption 

 to heat-killed bacteria. They concluded that either the incor- 

 poration of phage DNA into its membrane was the last stage in 

 maturation or else that the hypothetical immature DNA-con- 

 taining phage particles were structurally unstable and disinte- 

 grated during host cell lysis. Thus there were only two observable 

 forms of phage DNA that could be isolated from infected bac- 

 teria; free DNA in solution and DNA in fully infectious, mature 

 phage particles. 



Very detailed kinetic studies using P^^ gj-j^-j phage T4 were pub- 

 lished by Stent and Maal0e (1953). They concluded, in agree- 

 ment with Weed and Cohen (1951), that there was a greater 

 contribution of host cell materials to the earlier produced phage. 

 The first phage particles to mature received about 60 per cent 

 of their phosphorus from materials assimilated before infection. 

 About 70 to 80 per cent of the total available bacterial contribu- 

 tion had been incorporated into mature phage particles during 

 the first 30 minutes. Within a minute or two after infection the 

 rate of assimilation of phage-precursor phosphorus from the 

 medium increased by a factor of eight as compared with the rate 

 before infection. This is probably due in part to the elimination 

 of other uses for phosphorus such as synthesis of RNA (Cohen, 

 1952). The average time between the assimilation of phos- 

 phorus atoms and their incorporation into mature phage was 14 

 minutes with a minimum of 5 minutes. 



Kinetics of phosphorus assimilation in phage T6 were studied 

 by Labaw (1953) by introducing P^^ j^^q ^^^ bacterial culture 

 at various times before or after infection. Most of his results 

 with this phage are similar to those already described. One 

 observation is in disagreement with other findings. The phos- 

 phorus contribution of the host cell to the mature phage is a con- 

 stant value of about 30 per cent of the, phage phosphorus regard- 

 less of the time of lysis or the mean burst size. This is in direct 



