Interviewee: François Jacob. François Jacob talks about bacterial mutants that could not metabolize lactose. Using these mutants, Jacob and Monod figured out how protein production is controlled. (DNAi Location: Code > Controlling the code > Players > François Jacob and Jacques Monod > Making mutants)

Well, Monod started to make mutants, he made mutants which were unable to use lactose, that is to eat lactose and to metabolize lactose, and he showed that in these, some of these mutant there was no galactosidase made. So, that was a gene, which controlled the synthesis of galactosidase. Then they found also that there was another gene closely adjacent, which turned out to be adjacent to the first one, which had to do with the entry of lactose in the cell, and they called that permease. So, bacteria could become unable to utilize lactose, either because they were unable to make the enzyme, which cut the lactose, or because they became unable to concentrate lactose in the cell. In addition, in most wild type <i>E. coli</i>, that is the <i>E. coli</i> you find in nature or in the guts of all of us, the enzyme is inducible as we said, that is, it's made only in the presence of galactoside. But they also found, the Monod group found that there are mutants, which are able to make the enzyme without the galactoside. So the first one, which is the normal, we are call inducible, and the other one was called constitutive. And the question was, why is it constitutive?

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