BIOLOGICAL ORDER 



and persist in a prophage which is reproduced as nucleic acid and 

 which can be perpetuated without expressing its potentialities. 



The study of the behavior of the defective prophage after induc- 

 tion has revealed the existence of a set of functions controlling the 

 duplication of the viral nucleic acid. The existence of such functions 

 for the duplication of the cellular chromosome can only be postu- 

 lated. A strong argument in favor of this hypothesis is that in a cell 

 all the chromosomes divide not only at the right time but also at 

 the same time. Obviously, some unknown factor commands the 

 duplication of the chromosomes. 



In a bacterium, the chromosome and the prophage act as a whole. 

 The prophage behaves as if it were a bacterial element. Thus the 

 genetic material of a virus, when attached to a cellular organelle, 

 is submitted to the cellular system of control. 



The reverse is also true: a cellular gene may be under viral 

 command. The prophage is attached to a specific receptor site of 

 the bacterial chromosome. A part of the receptor of prophage A is 

 the gene that carries the information for galactokinase (the enzyme 

 that phosphorylates galactose). It happens that this gene galacto- 

 kinase can be exchanged with a part of phage A. The gene galacto- 

 kinase is now part of phage A, and when this phage A multiplies 

 vegetatively, the gene galactokinase multiplies too. 



In one case, the prophage behaves as if it were a bacterial gene. 

 In the other case, a bacterial gene behaves as if it were a viral gene. 

 This probably means that a given chromosome, whether cellular or 

 viral, and the "foreign" nucleic acid it may carry constitute a unit 

 and behave as a whole, so far as replication is concerned. 



The study of the functional order, of the induction and repres- 

 sion of enzyme synthesis, has revealed a different situation: the 

 various individual systems controlling enzyme synthesis are inde- 

 pendent in the sense that one may be blocked while the others are 

 working. The enzymes for tryptophan synthesis may be produced 

 while those for methionine synthesis are repressed. Are viruses able 

 to take command of cellular functions? The reader realizes of course 

 that the question would not be posed if a positive answer could not 

 be provided. 



Viral control of cellular functions. A nonlysogenic 

 Sahnojiella produces a given somatic antigen 10. If lysogenized 



[82] 



