Final answer:
Formation of an active RNAPII complex on a promoter requires the action of activators, which are proteins that enhance the interaction between RNA polymerase and the promoter. Enhancers, bound by activators, are instrumental in increasing the efficiency of gene expression.
Step-by-step explanation:
The formation of an active RNA polymerase II (RNAPII) complex on a promoter requires the action of activators. Activators are proteins that enhance the interaction between RNA polymerase and a particular promoter. A promoter is, by definition, a specific sequence of DNA nucleotides that is essential for the initiation of transcription. Enhancers are DNA sequences that increase the efficiency of gene expression by allowing for the interaction of activators with the transcription factors bound to the promoter region.
On the other hand, repressors and silencers negatively affect transcription. Repressors can bind to non-coding sequences to impede the progress of RNA polymerase, while silencers decrease the efficiency of transcription but are not strictly necessary for transcription to proceed. Ultimately, activators bound to enhancers play a crucial role in stabilizing the bend in the DNA that facilitates the initiation of transcription by RNA polymerase II.