VIRAL FUNCTIONS: ORDER AND DISORDER 



and a protection against the adverse conditions encountered in the 

 outer world. 



The virus. The nucleic acid of a number of viruses has been 

 extracted and purified. If properly handled and if not altered, it 

 may infect cells. The proof of the effectiveness of the infection is 

 the production by the infected cell of a new generation of virions. 

 The virus is reproduced from its genetic material only. At the 

 cellular level, a viral infection is the penetration into a cell of the 

 genetic material of a virus. 



The genetic material is RNA in some viruses, DNA in others. 

 A virion never contains both nucleic acids. Every cell, every micro- 

 organism without exception, possesses both types of nucleic acid, 

 RNA and DNA. An organized infectious entity possessing only one 

 type of nucleic acid can only be a virus. Moreover, reproduction 

 from the genetic material only is something which neither a cell 

 nor a microorganism can accomplish, and which is an essential and 

 specific feature of viruses. It is clear also that the genetic material of 

 a virus has to possess the information (a) for the synthesis of the pro- 

 teins of the viral coat, and (b) for autonomous reproduction. 



Remarks on the control of viral functions. When a cell is 

 infected by a virus, let us say poliovirus, viral proteins are synthe- 

 sized, and the genetic material is multiplied. This is the so-called 

 vegetative phase of the viral life cycle. Mrions, infective particles, 

 are not produced during the first phase. They -appear around the 

 third hour, and thereafter will increase in number. Approximately 

 6 to 8 hours after the infection each cell contains about 100,000 

 viral particles, among which only about 500 are infectious. As a 

 result of viral multiplication, the cell is damaged and finally dis- 

 integrates. 



In a normal, noninfected cell, the synthesis of cellular structures 

 is a well-ordered process. An elaborate system of repression and 

 induction based on a feedback mechanism controls the balanced 

 synthesis of enzymes. 



Viruses are sometimes considered as pathological particles of 

 cellular origin. Are viruses, like normal cellular constituents, subject 

 to a regulating system? If a viral regulating system does exist, how 

 do viral and cellular functions interact? The study of bacteriophage 

 should allow us to answer these questions. 



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