Replicon (genetics)

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A replicon is a DNA molecule or RNA molecule, or a region of DNA or RNA, that replicates from a single origin of replication. Replication of a genome is a self-regulatory process in which each genome or portion of a genome is replicated independently of any others. 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[citation needed]. Most prokaryotic genomes consist of a single replicon, whereas eukaryotic genomes consist of multiple replicons per chromosome and multiple chromosomes per genome.

Prokaryotes[]

For most prokaryotic chromosomes, the replicon is the entire chromosome. One notable exception 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 (two), Vibrio cholerae,[1] and Burkholderia multivorans (three). These "secondary" (or tertiary) chromosomes are often described as molecules that are intermediate between a true chromosome and a plasmid and are sometimes called "chromids". Various Azospirillum species possess seven replicons; A. lipoferum, for instance, has one bacterial chromosome, five chromids, and one 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. Known examples range in size from 10 to 330 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 eukaryote, Saccromyces cerevisiae. Therefore, no general picture of a replicon as replicator and initiator in eukaryotes has been achieved.

In the case of mitochondria, the definition of replicons is somewhat confused, as they use unidirectional replication with two separate origins.

Non-cellular entities[]

Non-cellular entities such as viruses, plasmids, transposons, retrotransposons, viroids, virusoids and RNA satellites 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.[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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