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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. [1] [2] These proteins are usually referred to as transcription factors. Enhancers are cis-acting. They can be located up to 1 Mbp (1,000,000 bp) away from the gene ...
Transcription factors can be divided in two main categories: activators and repressors. While activators can interact directly or indirectly with the core machinery of transcription through enhancer binding, repressors predominantly recruit co-repressor complexes leading to transcriptional repression by chromatin condensation of enhancer regions.
An enhancer localized in a DNA region distant from the promoter of a gene can have a very large effect on gene transcription, with some genes undergoing up to 100-fold increased transcription due to an activated enhancer. [10] Enhancers are regions of the genome that are major gene-regulatory elements.
The Hox transcription factor family, for example, is important for proper body pattern formation in organisms as diverse as fruit flies to humans. [24] [25] Another example is the transcription factor encoded by the sex-determining region Y (SRY) gene, which plays a major role in determining sex in humans. [26]
Enhancers are much more common in eukaryotes than prokaryotes, where only a few examples exist (to date). [4] Silencers are regions of DNA sequences that, when bound by particular transcription factors, can silence expression of the gene.
Enhancers and their associated transcription factors have a leading role in the regulation of gene expression. [65] Enhancers are genome regions that regulate genes. 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. [66]
A transcriptional activator is a protein (transcription factor) that increases transcription of a gene or set of genes. [1] Activators are considered to have positive control over gene expression, as they function to promote gene transcription and, in some cases, are required for the transcription of genes to occur.
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.