Based on these and other results, Monod proposed his now famous operon model. Other Pages Interpretations Monod's approach is an example of the genetic approach to understanding the regulation of transcription. Beta-galactosidase synthesis is an example of induction. A small molecule, a co-inducer , induces enzyme synthesis. Further information Repression systems, in which the presence of a small molecule, a co-repressor , turns gene expression off, also exist.
Inhibition is in part due to occlusion of the promoter .
In some other systems, examples of positive regulation, protein binding stimulates transcription. Positive regulation is thought to act by altering DNA conformation. The stimulated sensor activates the DNA-binding protein. The expression complex controlled by a single operator is called an operon . Multiple operons controlled by the same repressor or activator are called a regulon .