Furthermore, an enhancer doesn't need to be located near the transcription initiation site to affect transcription, as some have been found located several hundred thousand base pairs upstream or downstream of the start site. Silencers and enhancers may be in close proximity to each other or may even be in the same region only differentiated by the transcription factor the region binds to.Īn enhancer may be located upstream or downstream of the gene it regulates. Silencers are antagonists of enhancers that, when bound to its proper transcription factors called repressors, repress the transcription of the gene. The same mechanism holds true for silencers in the eukaryotic genome. This allows it to interact with the general transcription factors and RNA polymerase II.

In eukaryotic cells the structure of the chromatin complex of DNA is folded in a way that functionally mimics the supercoiled state characteristic of prokaryotic DNA, so although the enhancer DNA may be far from the gene in a linear way, it is spatially close to the promoter and gene.

This enhancer, located in the large intron, provided an explanation for the transcriptional activation of rearranged Vh gene promoters while unrearranged Vh promoters remained inactive. The first discovery of a eukaryotic enhancer was in the immunoglobulin heavy chain gene in 1983. They are found in both prokaryotes and eukaryotes. There are hundreds of thousands of enhancers in the human genome. They can be located up to 1 Mbp (1,000,000 bp) away from the gene, upstream or downstream from the start site. These proteins are usually referred to as transcription factors. In genetics, an enhancer is a short (50–1500 bp) region of DNA that can be bound by proteins ( activators) to increase the likelihood that transcription of a particular gene will occur.

Gene sequence definition biology