,The three types of regulatory molecules that can affect the expression of operons and thus transcription are: repressors, activators, and inducers. Repressors are proteins that suppress transcription of a gene in response to an external stimulus. In other words, a repressor keeps a gene “off.”
Activators are also the proteins which speed up the transcription process.
The binding of the inducer to the repressor prevents the repressor from binding to the operator. RNA polymerase can then begin to transcribe operon genes. Secondly it can exert its effect by binding to activators.