A eukaryotic gene has an enhancer located thousands of base pairs upstream of its promoter. A transcription factor (TF) bound at the enhancer associates with RNA polymerase II at the promoter via DNA looping.
What functional role do enhancer sequences play even when located far from the gene's promoter?
- A
They terminate transcription at long distances.
- Bcheck_circle
They serve as binding sites for activator proteins; DNA looping brings them to the promoter to stimulate transcription.
- C
They prevent splicing of the resulting pre-mRNA.
- D
They are translated by ribosomes to produce activator proteins.
Explanation
Enhancers are cis-regulatory elements bound by activators. DNA looping physically associates these activators with the basal transcription machinery at the promoter, increasing transcription frequency.