The Principle of Enzymic Induction

The system of induced synthesis of/ -galactosidase has served as basic model for years of research in several laboratories studying the mechanisms of this synthesis. The most widely known studies are those of Jacob and Monod, resulting in the creation of an experimentally based concept of regulation of genetic activity, which we shall describe briefly on the basis of the publications summarizing their conclusions (Jacob and Monod, 1963, 1964). 

In some cases structural genes are constantly active (constitutive synthesis), but in the case of the jS-galactosidase gene it has been showed that when lactose is absent from the medium the 

The essence of their experiments was to study mutants of E, coli in which the mutation affected this system (for example, the isolation of cells with constitutive ssmthesis of jS-galactosidase) and to determine the location of these mutations on the genetic map of E. coli. We shall examine techniques for the location of genes on the genetic map of E, coli a little later on. 

Jacob and Monod s concept of the mechanisms and systems of genetic regulation contains very many hypotheses, and before discussing their general pattern we must first examine the conclusions which can now be regarded as firmly established experimentally. 

Z-gene, the gene for jS-galactosidase, consisting of several structural cistrons forming polypeptide subunits of the protein, iS-galactosidase  

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