12 LURIA 



synthetic enzymes of the bacterium are responsible and rate-limiting 

 for the formation of the building blocks for phage synthesis. DNA 

 synthesis immediately precedes and parallels the appearance of active 

 phage particles and fails to take place in bacteria infected with inactive, 

 nonreactivated phage, which suggests that DNA may be involved 

 mainly in the final steps of the "baking" of active particles. Infection 

 with ultraviolet inactivated phage not leading to active phage produc- 

 tion is, however, accompanied by the production of some ultraviolet 

 absorbing material, as yet unidentified (28). It would be rash to in- 

 terpret these abortive syntheses as due to the activity of portions of 

 the infecting phage particles that are not damaged by ultraviolet 

 radiation. 



Failure of phage infected bacteria to produce specific bacterial com- 

 ponents, as distinct from phage substance, is shown by the elegant 

 experiment of Monod and Wollman (30) on the absence of adaptive 

 enzyme formation in phage-infected bacteria, A similar failure of en- 

 zymatic adaptation has been observed in bacteria infected by ultra- 

 violet inactivated phage under conditions in which no reactivation 

 occurs (27). 



A rationale for the suppression by phage infection of specific bac- 

 terial syntheses is suggested, in the light of current theories of gene 

 action, by cytological observations (28). The first result of infection 

 of a bacterium either with active or irradiated phage T2 is a rapid 

 disruption of its nuclear apparatus represented by the Feulgen-positive 

 "chromatin" bodies. In the case of infection with active phage, nuclear 

 disruption is followed by the appearance of a granular type of chroma- 

 tin which probably represents the new phage itself, as indicated by 

 the failure of this new chromatin to accumulate either after infection 

 with inactive, nonreproducing phage, or after infection with active 

 phage in certain abnormal bacterial strains which upon lysis fail to 

 produce any active phage. These observations suggest that the sup- 

 pression of synthesis of specific bacterial components in a phage in- 

 fected bacterium results from a disruption of the genetic apparatus of 

 the bacterium and its replacement with the genetic apparatus of the 

 virus, resulting in viral rather than bacterial specificity of the proto- 

 plasm newly synthesized by the available bacterial enzymatic ma- 

 chinery. The disruption of the genetic apparatus of bacteria infected 

 with inactive phage explains the failure of these bacteria to undergo 

 any further multiplication. 



According to this hypothesis, the virus does not only introduce into 

 the host bacterium an additional organizer of specificity, but a com- 



