VIRAL FUNCTIONS: ORDER AND DISORDER 



with a given phage e 15, it stops producing the antigen 10, and in 

 turn produces another antigen 15. The mechanism by which pro- 

 phage 15 controls the synthesis of a bacterial antigen is still a 

 mvsterv. 



A much more fascinating situation has been disclosed with galacto- 

 kinase. A short digression is necessary here. The gene galactokinase 

 and the prophage A are closely linked. Both may be attached to the 

 sexual factor F, and thus transferred from the male to the female. 

 If the partners are properly selected, a large variety of heterozygotes 

 may be obtained. It happens that in the absence of an inducer the 

 bacteria contain only a small amount of galactokinase. A marked 

 synthesis of the enzyme takes place only when an inducer is present. 

 But when phage A develops vegetatively, either as a result of an 

 infection or as a consequence of an induction, then the enzyme 

 galactokinase is synthesized in large amounts in the absence of an 

 inducer. This synthesis takes place only when the gene and the 

 phage are in position cis (when they are part of the same structure), 

 and not in position trans (when they are in different structures). 



Things happen here as if the bacterial gene were obeying some 

 viral mechanism of control, perhaps a viral operator. Thus a virus 

 may be subject to the control system of a bacterium, and a bac- 

 terial gene to the control system of a virus, both for replication 

 and for expression. 



Viral and noxviral diseases. When a defective lysogenic bac- 

 terium is induced, the defective prophage is derepressed. An abnor- 

 mal vegetative phase is initiated. Bacteriophage particles are not 

 produced, but the bacterium nevertheless dies. The disease is not the 

 result of an infection, and infectious particles have not been formed. 

 Strictly speaking, the disease is not viral. The defective prophage 

 possesses some of the normal viral genes but behaves as a potential 

 lethal gene (Table VIII). A few hereditary, nonviral diseases of 

 bacteria are known which are controlled not by a defective prophage 

 but by genetic structures that have to be visualized as bacterial genes, 

 potentially lethal genes. Between these hereditary diseases and viral 

 diseases, an almost complete series of intermediary steps has been 

 disclosed, and the hypothesis that the genetic material of viruses has 

 evolved from cellular genes is currently admitted. 



Viruses and cancer. Thus a virus may be multiplied as genetic 



[83] 



