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In genetics, an enhancer is a short (50–1500 bp) region of DNA that can be bound by proteins to increase the likelihood that transcription of a particular gene will occur.
A transcribed enhancer RNA (eRNA) interacting with the complex of Mediator proteins (see Figure), especially Mediator subunit 12 , appears to be essential in forming the chromosome loop that brings the enhancer into close association with the promoter of the target gene of the enhancer in the case of five genes studied by Lai et al. [15] [16 ...
The best known example of the enhanceosome acts on the human interferon-beta gene, which is upregulated in cells that are infected by viruses. [5] Three activator proteins— NF-κB , an interferon activator protein such as IRF-3 , and the ATF -2/c-Jun complex—cooperatively bind to the upstream enhancer region upon viral infection.
Enhancers are sequences of the genome that are major gene-regulatory elements. Enhancers control cell-type-specific gene expression programs, most often by looping through long distances to come in physical proximity with the promoters of their target genes. [6]
Super-enhancers may have evolved at key cell identity genes to render the transcription of these genes responsive to an array of external cues. [44] The enhancers comprising a super-enhancer can each be responsive to different signals, which allows the transcription of a single gene to be regulated by multiple signaling pathways. [44]
Enhancers are CREs that influence (enhance) the transcription of genes on the same molecule of DNA and can be found upstream, downstream, within the introns, or even relatively far away from the gene they regulate. Multiple enhancers can act in a coordinated fashion to regulate transcription of one gene. [7]
Whereas one could think that there is a 1:1 enhancer-promoter ratio, studies of the human genome predict that an active promoter interacts with 4 to 5 enhancers. Similarly, enhancers can regulate more than one gene without linkage restriction and are said to “skip” neighboring genes to regulate more distant ones.
The link between E-box-regulated genes and the circadian clock was discovered in 1997, when Hao, Allen, and Hardin (Department of Biology at Texas A&M University) analyzed rhythmicity in the period gene in Drosophila melanogaster. [16] They found a circadian transcriptional enhancer upstream of the per gene within a 69 bp DNA fragment.