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{{Short description|DNA region replicating from a single origin}}
A '''replicon''' is a region of an organism's genome that is independently replicated from a single [[origin of replication]]{{Citation needed|reason=definition|date=April 2023}}. A bacterial chromosome contains a single origin, and therefore the whole bacterial chromosome is a replicon. The chromosomes of [[archaea]] and [[Eukaryote|eukaryotes]] can have multiple origins of replication, and so their chromosomes may consist of several replicons{{Citation needed|reason=definition|date=April 2023}}. The concept of the replicon was formulated in 1963 by [[François Jacob]], [[Sydney Brenner]], and Jacques Cuzin as a part of their replicon model for replication initiation. According to the replicon model, two components control replication initiation: the replicator and the initiator. The replicator is the entire DNA sequence (including, but not limited to the origin of replication) required to direct the initiation of DNA replication. The initiator is the protein that recognizes the replicator and activates replication initiation.<ref>{{Cite book|url=https://www.worldcat.org/oclc/824087979|title=Molecular Biology of the Gene |date=2014|publisher=Cold Spring Harbor Laboratory Press| vauthors = Watson JD |isbn=978-0-321-76243-6|edition=7|location=Boston|pages=288–289|oclc=824087979}}</ref>
Sometimes in [[bacteriology]], the term "replicon" is only used to refer to chromosomes containing a single origin of replication and therefore excludes the genomes of [[archaea]] and [[Eukaryote|eukaryotes]] which can have several origins.<ref>{{cite journal | vauthors = diCenzo GC, Finan TM | title = The Divided Bacterial Genome: Structure, Function, and Evolution | journal = Microbiology and Molecular Biology Reviews | volume = 81 | issue = 3 | date = September 2017 | pmid = 28794225 | pmc = 5584315 | doi = 10.1128/MMBR.00019-17 }}</ref>
==Prokaryotes==
For most [[prokaryotic]] [[chromosomes]], the replicon is the entire chromosome. One notable exception
[[Plasmid]]s and [[bacteriophage]]s are usually replicated as single replicons, but large plasmids in [[Gram-negative bacteria]] have been shown to carry several replicons.<ref name="Thomas200">{{Cite book| edition = 1| publisher = CRC Press| isbn = 9057024624|
== Eukaryotes ==▼
For [[eukaryotic]] chromosomes, there are multiple replicons per chromosome. Known examples range in size from 10 to 330 [[Kilobase|kilobases]]. A cluster of replicons replicates simultaneously. But different clusters start replicating at different times during [[S phase]], depending on their location along the chromosomes. In general, clusters nearer the [[centromere]] replicate earlier. Fine structure analysis of chromosomal origins of replication is limited to a single [[Model organism|model]] eukaryote, ''Saccharomyces cerevisiae''. Therefore, no general picture of a replicon as replicator and initiator in eukaryotes has been achieved.
==Non-cellular entities==
▲==Eukaryotes==
[[Non-cellular life|Non-cellular entities]] such as [[virus]]es, [[plasmid]]s, [[transposon]]s, [[retrotransposon]]s, [[viroid]]s, [[virusoid]]s and [[Satellite (biology)|RNA satellite]]s are also replicons. [[Patrick Forterre]] of the [[Pasteur Institute]] has coined the term "orphan replicon" to refer to those that are not viruses; i.e., that lack a [[capsid]].<ref name="RaoultForterre2008">{{cite journal | vauthors = Raoult D, Forterre P | title = Redefining viruses: lessons from Mimivirus | journal = Nature Reviews. Microbiology | volume = 6 | issue = 4 | pages = 315–319 | date = April 2008 | pmid = 18311164 | doi = 10.1038/nrmicro1858 | s2cid = 24447407 }}</ref>
▲For eukaryotic chromosomes, there are multiple replicons per chromosome. The definition of replicons is somewhat confused with [[Mitochondrion|mitochondria]], as they use unidirectional replication with two separate origins.
== See also ==
* [[DNA replication]]
* [[Origin of replication]]
* [[Secondary chromosome]]
== References ==
{{reflist}}
{{DNA replication|state=expanded}}
{{Self-replicating organic structures|state=collapsed}}
[[Category:DNA replication]]
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