Synthesis of a repressible enzyme is stopped by the corepressor-repressor binding to the operator.
When the end product of the reaction that catalyzes the enzyme prevents its synthesis, this phenomenon is called negative induction.
When the controlling substance is attached to the repressor molecule, it sticks to the promoter, preventing the transcription of the gene, and therefore, turning it off, the compound that prevents the synthesis of the enzyme is called a co-repressor.
In said negative induction, the repressor is inactive, but in the presence of the corepressor it is activated (acquires its functional capacity), and that is when it represses the structural operon.
Repressible systems correspond to synthesis or anabolism processes, for example the tryptophan operon and the histine operon.
The trp operon is an example of the genetic regulation of repressible enzymes, because the presence of the product of the metabolic pathway represses or inhibits the synthesis of the enzymes necessary to synthesize it.
Technically, the controller (tryptophan), is called a corepressor, because it works with the repressor to block transcription, it is then a negative control mechanism.
Therefore, we can conclude that synthesis of a repressible enzyme is stopped by the corepressor-repressor binding to the operator.
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