For most prokaryotic chromosomes, the replicon is the entire chromosome. One notable exception found comes from archaea, where two Sulfolobus species have been shown to contain three replicons. Examples of bacterial species that have been found to possess multiple replicons include: Rhodobacter sphaeroides (2), Vibrio cholerae, and Burkholderia multivorans (3). These "secondary" (or tertiary) chromosomes are often described as a molecule that is a mixture between a true chromosome and a plasmid and are sometimes called "chromids". Various Azospirillum species possess 7 replicons, Azospirillum lipoferum, for instance, has 1 bacterial chromosome, 5 chromids, and 1 plasmid.Plasmids and bacteriophages are usually replicated as single replicons, but large plasmids in Gram-negative bacteria have been shown to carry several replicons.
For eukaryotic chromosomes, there are multiple replicons per chromosome. In the case of mitochondria the definition of replicons is somewhat confused, as they use unidirectional replication with two separate origins.
Non-cellular entities such as viruses, plasmids, transposons, retrotransposons, viroids, virusoids and RNA satellites are 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.
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- Thomas, Christopher M. (2000-05-01). Horizontal Gene Pool: Bacterial Plasmids and Gene Spread (1 ed.). CRC Press. ISBN 9057024624.
- Raoult, Didier; Forterre, Patrick (2008). "Redefining viruses: lessons from Mimivirus". Nature Reviews Microbiology. 6 (4): 315–319. doi:10.1038/nrmicro1858. ISSN 1740-1526.