Editing Operon (section)

{{Short description|Group of open reading frames under the same regulation}}
{{Distinguish|Opteron|Oberon}}
[[File:Operon 1.png|thumb|350px|right|A typical operon]]
In [[genetics]], an '''operon''' is a functioning unit of [[DNA]] containing a cluster of [[gene]]s under the control of a single [[promoter (genetics)|promoter]].<ref>{{cite book | first1 = David E. | last1 = Sadava | first2 = David M. | last2 = Hillis | first3 = H. Craig | last3 = Heller | first4 = May | last4 = Berenbaum | name-list-style = vanc |title=Life: The Science of Biology |publisher=Macmillan|year=2009 |edition=9th |isbn=978-1-4292-1962-4 |page=349 |url=https://books.google.com/books?id=ANT8VB14oBUC&pg=PA349 }}</ref> The genes are [[transcription (biology)|transcribed]] together into an [[Messenger RNA|mRNA]] strand and either [[translation (biology)|translated]] together in the cytoplasm, or undergo [[RNA splicing|splicing]] to create [[Cistron|monocistronic]] mRNAs that are translated separately, i.e. several strands of mRNA that each encode a single gene product. The result of this is that the genes contained in the operon are either [[gene expression|expressed]] together or not at all. Several genes must be ''co-transcribed'' to define an operon.<ref>{{cite book | last1=Lodish | first1=Harvey | last2=Zipursky | first2=Lawrence | last3=Matsudaira | first3=Paul | last4=Baltimore | first4=David | last5=Darnel | first5=James | name-list-style=vanc | title=Molecular Cell Biology | publisher=W. H. Freeman | year=2000 | chapter=Chapter 9: Molecular Definition of a Gene | isbn=978-0-7167-3136-8 | url=https://archive.org/details/molecularcellbio00lodi }}</ref>

Originally, operons were thought to exist solely in [[prokaryote]]s (which includes [[organelle]]s like [[plastid]]s that are derived from [[bacteria]]), but their discovery in [[eukaryote]]s was shown in the early 1990s, and are considered to be rare.<ref name="Kominek">{{cite journal |vauthors=Kominek J, Doering DT, Opulente DA, Shen XX, Zhou X, DeVirgilio J, Hulfachor AB, Groenewald M, Mcgee MA, Karlen SD, Kurtzman CP, Rokas A, Hittinger CT |title=Eukaryotic Acquisition of a Bacterial Operon |journal=Cell |volume=176 |issue=6 |pages=1356–1366.e10 |date=March 2019 |pmid=30799038 |pmc=7295392 |doi=10.1016/j.cell.2019.01.034 |url=}}</ref><ref>{{cite journal | vauthors = Spieth J, Brooke G, Kuersten S, Lea K, Blumenthal T | title = Operons in C. elegans: polycistronic mRNA precursors are processed by trans-splicing of SL2 to downstream coding regions | journal = Cell | volume = 73 | issue = 3 | pages = 521–32 | date = May 1993 | pmid = 8098272 | doi = 10.1016/0092-8674(93)90139-H | s2cid = 26918553 }}</ref><ref>{{cite journal | vauthors = Brogna S, Ashburner M | title = The Adh-related gene of Drosophila melanogaster is expressed as a functional dicistronic messenger RNA: multigenic transcription in higher organisms | journal = The EMBO Journal | volume = 16 | issue = 8 | pages = 2023–31 | date = April 1997 | pmid = 9155028 | pmc = 1169805 | doi = 10.1093/emboj/16.8.2023 }}</ref><ref name="Operons in eukaryotes">{{cite journal | vauthors = Blumenthal T | title = Operons in eukaryotes | journal = Briefings in Functional Genomics & Proteomics | volume = 3 | issue = 3 | pages = 199–211 | date = November 2004 | pmid = 15642184 | doi = 10.1093/bfgp/3.3.199 | doi-access = free }}</ref> In general, expression of prokaryotic operons leads to the generation of [[Cistron|polycistronic]] mRNAs, while eukaryotic operons lead to monocistronic mRNAs.

Operons are also found in viruses such as [[bacteriophage]]s.<ref>{{cite web| title=Definition of Operon| url=http://www.medterms.com/script/main/art.asp?articlekey=32917| work=Medical Dictionary| publisher=MedicineNet.com| access-date=30 December 2012}}</ref><ref name="Liu_2004">{{cite journal | vauthors = Liu J, Mushegian A | title = Displacements of prohead protease genes in the late operons of double-stranded-DNA bacteriophages | journal = Journal of Bacteriology | volume = 186 | issue = 13 | pages = 4369–75 | date = July 2004 | pmid = 15205439 | pmc = 421614 | doi = 10.1128/JB.186.13.4369-4375.2004 }}</ref> For example, [[T7 phage]]s have two operons. The first operon codes for various products, including a special [[T7 RNA polymerase]] which can bind to and transcribe the second operon. The second operon includes a [[lysis]] gene meant to cause the host cell to burst.<ref>{{cite web|title=Bacteriophage Use Operons|url=http://www.dartmouth.edu/~cbbc/courses/bio4/bio4-lectures/ProkGeneControl.html|work=Prokaryotic Gene Control|publisher=Dartmouth College|access-date=30 December 2012|archive-url=https://web.archive.org/web/20130128061441/http://www.dartmouth.edu/~cbbc/courses/bio4/bio4-lectures/ProkGeneControl.html|archive-date=28 January 2013|url-status=dead}}</ref>