What is an enhancer and how does it influence transcription?

• A. An enhancer is a DNA element that, when bound by activators, increases transcription from a promoter, often at a distance and in an orientation-independent manner.
• B. An enhancer is a protein complex that binds promoter to start transcription.
• C. An enhancer is a RNA molecule that decoys transcription factors.
• D. An enhancer is a DNA sequence that blocks transcription when bound by repressors.

Answer: (A)

Enhancers are DNA elements that increase transcription by binding activator proteins. They can act from a distance and in any orientation, reaching the promoter through looping so the activators can interact with the transcription machinery at the start site. This looping and contact with coactivators help recruit RNA polymerase II and other factors, boosting transcription initiation. Enhancers often work in a tissue-specific way because different combinations of activators are present in different cells, giving precise control over when and where a gene is expressed.

Other ideas don’t fit because a promoter-proximal protein complex starts transcription at the promoter itself, not from a distant DNA element. An RNA molecule that decoys transcription factors isn’t an enhancer. A DNA sequence that blocks transcription when bound by repressors describes a silencer, not an enhancer.