100 Essays in Biochemistry 



5-HMC (synthesized in part from the cytosine of the host), then this 

 material is synthesized from the simple components of the medium. 

 There is little or no utilization of bacterial protein or amino acids for 

 virus synthesis so that viral protein is formed largely by de novo 

 synthesis from the components of the medium. 



Immediately after infection with virulent coliphages, one observes 

 changes in both the morphology and enzymic spectrum of the infected 

 cells. The cytological effects involve abnormal alterations in the chro- 

 matinic or nuclear material of the bacterial cell, as one might suspect 

 on the basis of the chemical changes in nucleic acid metabolism. The 

 oxygen uptake is unchanged, but the metabolism of both the phospho- 

 lipide and the RNA fractions appears to cease, insofar as these con- 

 stituents of the host cell show no further incorporation of phosphate 

 after infection. As viral DNA is synthesized, the necessary deoxy- 

 ribose is derived from an increased rate of formation from triose 

 phosphate and acetaldehyde. Whether this involves an increase in the 

 actual amount of the enzyme systems involved, or whether their activ- 

 ity is enhanced, possibly by the loss of some inhibitory effect, is 

 unknown. In the case of DNAase activity, an apparent increase in 

 enzymic action can be shown to involve the loss of a specific inhibitor 

 which appears to be a ribose nucleic acid. If this should be a general 

 phenomenon, it would be a matter of the greatest interest for our 

 understanding of the metabolic role of RNA. However, we have no 

 knowledge of the cellular role of the DNAase itself, and, in view 

 of our incomplete information of the enzymic changes that take place 

 during infection, it is difficult to estimate the significance of the few 

 which have been described. 



The picture of virulent coliphage infection which emerges from all 

 this is one in which the process of virus synthesis is set off by a 

 fragment of the original infecting particle. The machinery that is 

 used for virus synthesis is the normal metabolic equipment of the 

 bacterial cell, and the materials on which it operates are the normal 

 components of the bacterial environment and certain portions of the 

 bacterial intracellular fabric. Many, if not all, of the normal metabolic 

 functions of the bacterial cell cease, and there begins an immediate 

 and rapid synthesis of the specific parts of the virus particle. Viral 

 DNA appears so rapidly after infection has occurred that it is difficult 

 to decide whether new enzymic machinery is synthesized for this pur- 

 pose, oi' whether a variation in some normal process occurs. Viral 

 protein can be detected somewhat later, but apparently the two com- 



