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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 ...
eRNAs are transcribed from DNA sequences upstream and downstream of extragenic enhancer regions. [8] Previously, several model enhancers have demonstrated the capability to directly recruit RNA Pol II and general transcription factors and form the pre-initiation complex (PIC) prior to the transcription start site at the promoter of genes.
Remote enhancers allow transcription regulation at a distance. Insulators situated between enhancers and promoters help define the genes that an enhancer can or cannot influence. Eukaryotic transcriptional activators have separate DNA-binding and activating functions. [ 1 ]
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.
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.
Multiple enhancers can act in a coordinated fashion to regulate transcription of one gene. [7] A number of genome-wide sequencing projects have revealed that enhancers are often transcribed to long non-coding RNA (lncRNA) or enhancer RNA (eRNA), whose changes in levels frequently correlate with those of the target gene mRNA. [8]
[3] [4] They found that a region of 140 base pairs in the tissue-specific transcriptional enhancer element was sufficient for different levels of transcription enhancement in different tissues and sequences. They suggested that proteins made by specific tissues acted on these enhancers to activate sets of genes during cell differentiation.
Enhancers are bound by transcription activator proteins and transcriptional regulation is typically controlled by more than one activator. Enhanceosomes are formed in special cases when these activators cooperatively bind together along the enhancer sequence to create a distinct three-dimensional structure.