enhancer

An enhancer is like a volume knob that can be wired to a speaker far down the hall. It is a piece of regulatory DNA that boosts how much a gene is transcribed — but, strikingly, it can sit thousands of bases away from the gene, even on the other side of it.

Enhancers work because DNA is flexible. Activator proteins bind the enhancer, and the DNA loops around so the enhancer is brought physically close to the gene's promoter, where it helps recruit and stabilise the transcription machinery. A single gene may answer to several enhancers, each active in a different tissue or condition, which is one reason the same gene can be expressed differently in different cells.

Because enhancers act at a distance and in a cell-type-specific way, they are central to development and a frequent site of trouble: mutations in an enhancer can raise or lower a gene's expression without touching the gene's own coding sequence, contributing to disease and to natural differences between individuals.