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{{Short description|Biological protein}}[[File:Enhanceosome_vertical.png|thumb|Structural model of the enhanceosome. Double-stranded [[DNA]] is shown in green and pink; the ATF-2/[[c-Jun]] [[coiled-coil]] DNA binding domain is shown in purple; [[interferon response factor]]s are shown in beige; and [[NF kappa B]] is shown in orange (p105 subunit) and blue (p65 subunit). ]]

An enhanceosome is a protein complex that assembles at an [[Enhancer (genetics)|enhancer region]] on DNA and helps to regulate the expression of a target gene.<ref name=":0">{{Cite journal |last1=Merika |first1=Menie |last2=Thanos |first2=Dimitris |date=2001-04-01 |title=Enhanceosomes |url=https://www.sciencedirect.com/science/article/pii/S0959437X00001805 |journal=Current Opinion in Genetics & Development |language=en |volume=11 |issue=2 |pages=205–208 |doi=10.1016/S0959-437X(00)00180-5 |pmid=11250145 |issn=0959-437X|url-access=subscription }}</ref>

== Formation ==
Enhancers are bound by [[Activator (genetics)|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. Each enhanceosome is unique towards its specific enhancer. This assembly is facilitated by energetically favorable [[Protein–protein interaction|protein: protein]] and protein: DNA interactions. Therefore, all the necessary activators need to be present for the enhanceosome to be formed and able to function.<ref name=":0" />

== Function ==
Once the enhanceosome has been formed, it recruits [[Coactivator (genetics)|coactivators]] and [[General transcription factor|general transcription factors]] to the [[Promoter (genetics)|promoter region]] of the target gene to begin transcription.<ref>{{Cite journal |last=Carey |first=Michael |date=1998-01-09 |title=The Enhanceosome and Transcriptional Synergy |journal=Cell |language=English |volume=92 |issue=1 |pages=5–8 |doi=10.1016/S0092-8674(00)80893-4 |pmid=9489694 |s2cid=16814171 |issn=0092-8674|doi-access=free }}</ref> The effectiveness of this is dependent on DNA conformation. As a result, the enhanceosome also recruits non histone architectural transcription factors, called [[High-mobility group|high-mobility group (HMG) proteins]], which are responsible for regulating [[chromatin]] structure.<ref>{{Cite journal |last1=Das |first1=Chandrima |last2=Kundu |first2=Tapas |date=2005-03-01 |title=Transcriptional Regulation by the Acetylation of Nonhistone Proteins in Humans – A New Target for Therapeutics |url=http://doi.wiley.com/10.1080/15216540500090629 |journal=IUBMB Life (International Union of Biochemistry and Molecular Biology: Life) |volume=57 |issue=3 |pages=137–149 |doi=10.1080/15216540500090629 |pmid=16036576 |s2cid=28252435 |issn=1521-6543|url-access=subscription }}</ref> These factors do not bind to the enhancer, but instead are used to restructure the DNA to ensure that the genes can be accessed by the transcription factors.

== Role ==
Most enhanceosomes have been discovered pertaining to genes requiring tight regulation, like those associated with the cells defense system.<ref>Cox, M. M., Doudna, J., & O’Donnell, M. (2015). Molecular Biology Principles and Practice (2nd ed.) W.H. Freeman and Company. {{ISBN|978-1-4641-2614-7}}</ref> Using more than one kind of transcriptional activator protein could help to ensure that a gene is not transcribed prematurely. Furthermore, the use of multiple factors enables gene regulation through a combination of cellular stimuli that function through multiple [[Signaling cascade|signaling cascades.]]

== Examples ==

=== IFN-β ===
The best known example of the enhanceosome acts on the [[human]] [[interferon-beta]] gene, which is upregulated in cells that are infected by [[virus]]es.<ref name=Panne>{{cite journal |last=Panne |first=D |title=The enhanceosome |journal=Current Opinion in Structural Biology |date=April 2008 |volume=18 |issue=2 |pages=236–42 |pmid=18206362 |doi=10.1016/j.sbi.2007.12.002}}</ref> Three activator proteins—[[NF-κB]], an interferon activator protein such as [[IRF-3]], and the [[Activating transcription factor|ATF]]-2/c-Jun complex—cooperatively bind to the upstream enhancer region upon viral infection. The interaction is mediated by a fourth protein [[High-mobility group|HMG-I]], which assists in stabilizing the complex by promoting inter-protein interactions. The assembled enhanceosome recruits transcriptional machinery such as [[RNA polymerase]] to the promoter region to initiate [[gene expression]].<ref name=":0" /><ref name=Panne/><ref>{{Cite journal|last1=Ford|first1=Ethan|last2=Thanos|first2=Dimitris|date=2010-03-01|title=The transcriptional code of human IFN-β gene expression|url=https://www.sciencedirect.com/science/article/pii/S1874939910000210|journal=Biochimica et Biophysica Acta (BBA) - Gene Regulatory Mechanisms|series=Chromatin in viral Gene Expression|language=en|volume=1799|issue=3|pages=328–336|doi=10.1016/j.bbagrm.2010.01.010|pmid=20116463 |issn=1874-9399|url-access=subscription}}</ref>

== References ==
{{reflist}}

== External links ==
* [http://pdb101.rcsb.org/motm/122 Enhanceosome] Molecule of the Month (February 2010) by David Goodsell

[[Category:Genetics]]

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