Answer:
Promoter:
Promoter may be defined as the region of DNA that are responsible for the transcription initiation of a gene. Promoters are located on the upstream region of DNA. RNA polymerase binds to the site of promoter.
Activator:
Activators are the factors that are responsible for the activation of transcription initiation. These factors helps in the binding of polymerase with the promoter region.
Repressor:
Repressors are the factors that decreases the rate of transcription. The presence of a repressor inhibits the binding of the RNA polymerase with the promoter.