Replicon (genetics)

A replicon is a DNA molecule or RNA molecule, or a region of DNA or RNA, that replicates from a single origin of replication.

Prokaryotes

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,[1] 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.[2] Plasmids and bacteriophages are usually replicated as single replicons, but large plasmids in Gram-negative bacteria have been shown to carry several replicons.[3]

Eukaryotes

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. DNA replication of a genome is a self regulatory process in which each genome or portion of a genome is replicated independently of each other .Such a unit of replication is called a replicon. Jacob, Brenner and Cuzin defined a replicon as the unit in which the cell controls individual acts of replication. 1- The genome of eukaryotes are composed of multiple simultaneously. They have variable size 10 to 330 kbp. 2- A cluster of replicons are replicated simultaneously. But different clusters at varying times clusters during S phase, depending on their location along the chromosomes. In General, clusters near the centromere replicate early. 3- fine structure analysis of chromosomal origins is limited to a single species of eukaryotes,''Saccromyces cerevisiae.Therefore, no general picture of a replicon as replicator and initiator in eukaryotes has been devised.

Non-cellular entities

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.[4]

See also

References
  1. Tagomori, K.; Iida, T.; Honda, T. (2002). "Comparison of genome structures of vibrios, bacteria possessing two chromosomes". Journal of Bacteriology. 184 (16): 4351–4358. doi:10.1128/JB.184.16.4351-4358.2002. PMC 135242. PMID 12142404.
  2. Wisniewski-Dyé, F.; Borziak, K.; Khalsa-Moyers, G.; Alexandre, G.; Sukharnikov, L. O.; Wuichet, K.; Hurst, G. B.; McDonald, W. H.; Robertson, J. S.; Barbe, V.; Calteau, A.; Rouy, Z.; Mangenot, S.; Prigent-Combaret, C.; Normand, P.; Boyer, M.; Siguier, P.; Dessaux, Y.; Elmerich, C.; Condemine, G.; Krishnen, G.; Kennedy, I.; Paterson, A. H.; González, V.; Mavingui, P.; Zhulin, I. B. (2011). Richardson, Paul M (ed.). "Azospirillum Genomes Reveal Transition of Bacteria from Aquatic to Terrestrial Environments". PLOS Genetics. 7 (12): e1002430. doi:10.1371/journal.pgen.1002430. PMC 3245306. PMID 22216014.
  3. Thomas, Christopher M. (2000-05-01). Horizontal Gene Pool: Bacterial Plasmids and Gene Spread (1 ed.). CRC Press. ISBN 9057024624.
  4. Raoult, Didier; Forterre, Patrick (2008). "Redefining viruses: lessons from Mimivirus". Nature Reviews Microbiology. 6 (4): 315–319. doi:10.1038/nrmicro1858. ISSN 1740-1526.


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