enhancer

Enhancer sequences are regulatory DNA sequences that, when bound by specific proteins called transcription factors, enhance the transcription of an associated gene. Regulation of transcription is the most common form of gene control, and the activity of transcription factors allows genes to be specifically regulated during development and in different types of cells.

Transcription factors can bind to enhancer sequences located upstream or downstream from an associated gene, resulting in stimulation or enhancement of transcription of the related gene. Enhancer sequences act upon genes on the same DNA molecule; however, enhancer sequences can be located thousands of base pairs away from the transcription start site of the gene being regulated. Because DNA is folded and coiled in the nucleus, the enhancer may actually be located near the transcription start site in the folded state. Additionally, enhancer sequences can be positioned in both forward or reversed sequence orientations and still affect gene transcription.