226 BACTERIOPHAGES 



d. Physical Slate of Parental Isotope during Transfer 

 The above experiments demonstrate that constituents of 

 parental nucleic acid appear in progeny particles. They do not 

 directly tell us, however, whether the transfer occurs by way of 

 genetically specific macromolecules or whether the parental DNA 

 is first degraded to low molecular weight nucleic acid precursors. 

 KozlofT favored the latter route, largely because of his observa- 

 tions of transfer unconnected with genetic transfer. Hershey 

 and Burgi's experiments cited above destroy the force of this 

 argument. Another possible way of deciding between these 

 alternatives is to examine the physical state of the parental 

 isotope during various stages of the latent period. This was done 

 by Watanabe, Stent, and Schachman (1954) who broke open 

 infected bacteria by decompression and examined the sensitivity 

 to deoxyribonuclease and sedimentation characteristics of the 

 intracellular isotope. At all times over 50 per cent of the P^^ 

 was in high molecular weight form, either as fibrous DNA or as 

 part of mature phage particles. In all their experiments some 

 isotope was observed in low molecular weight material, partly 

 owing to suboptimal conditions of viral growth. Their experi- 

 ments (which had another purpose) thus failed to answer the 

 question asked here. All observations of this type are com- 

 patible with breakdown of parental DNA if we allow for the 

 possibility of very rapid resynthesis into genetically specific 

 material. 



Hershey, Garen, Fraser, and Hudis (1954) made sev^eral at- 

 tempts to find evidence for possible short-lived intermediates. 

 By growing infected bacteria in the presence of large amounts of 

 nucleic acid precursors, they tried to influence the outcome of 

 transfer experiments with C^Mabeled T2. Even though free 

 bases and nucleosides compete efficiently with CO2 and glucose 

 as a source of viral DNA carbon, they are without effect on 

 parent to progeny transfer when added to cultures infected with 

 labeled phage. The same amount of parental G^^ is transferred 

 to the progeny irrespective of the amount of precursors added to 

 the infected system. Not only is the total transfer of QV^ the 



