104 Essays in Biochemistry 



the synthesis of DNA during the first phase of the latent period in 

 the induced cells. However, we have no specific marker for viral 

 DNA in the latter case such as 5-HMC in the case of the T-even 

 virulent coliphages; the data quoted relate to total DNA. 



It would seem that a comparative study of the induced Lysogenic 

 and virulent systems would he a matter of the greatest interest in 

 regard to a further understanding of the reactions involved in viral 

 synthesis. There appear to be greater synthetic limitations in the 

 virulent system, although virus synthesis has a preferential claim on 

 the energy and material sources available to the infected cell in both 

 virulent and temperate infections. 



In the case of both virulent and temperate infections, the evidence 

 points to reactions involving the genetic material of the cell. One 

 would suspect, therefore, a considerable degree of analogy between the 

 reactions we have described and those which occur in the course of 

 the normal growth and division of the bacterial cell. If the effective 

 portion of the virulent virus takes over and modifies the synthetic 

 reactions leading to the formation of viral DNA, it seems probable 

 that this material must bear a definite resemblance both in structure 

 and function to normal intermediates in cellular metabolism. When 

 one considers the complexity of the process and the product in which 

 viral DNA is neatly wrapped up into little parcels of protective protein, 

 one might expect again that there should be normal counterparts for 

 such structures. One would like to know something of the structure 

 and cellular location of the normal nucleoproteins of the bacterial cell. 

 At a more detailed level, one might also ask whether the synthesis 

 of the specific viral protein (in which the protein of the infecting 

 particle apparently does not participate) producing a material capable 

 of specific binding to certain portions of the bacterial cell wall does 

 not reflect the normal role of those particular bacterial enzymes used 

 in its manufacture. 



As our understanding of coliphage replication increases, the new facts 

 emphasize the intimate relations between this process and the normal 

 life of the bacterial cell itself. Although it is difficult to conceive any 

 physiological advantage in the lytic infection, and one may regard it 

 as a malignant variation of some normal process, there are a number 

 of phenomena associated with lysogeny which hint at some possible 

 biological role, even though it is not possible to grasp just what this 

 might be. In the case of certain strains of diphtheria bacteria which 

 do not produce toxin, lysogenization with an appropriate bacteriophage 

 leads to the prophage-carrying cells producing toxin. Again, bacterio- 



