Replicon is a molecule or region of DNA or RNA that replicates from one point of origin of replication .
The hypothesis of a replicon as a unit of replication was first expressed by F. Jacob , S. Brenner, and F. Cousin in 1964. According to the classical formulation of this hypothesis, each (prokaryotic) chromosome is a replication unit that is controlled by two elements: a cis-regulatory element by a replicator and a trans-regulatory element by an initiator , which is encoded by the chromosome and stimulates replication upon binding to the replicator [1] .
Subsequent studies have shown that this replicon hypothesis describes well the replication of bacterial chromosomes, bacterial plasmids , archaea and eukaryotes , as well as viruses and bacteriophages . It was found that the position of the origin of replication, that is, the DNA sections from which replication begins, coincides with the position of the replicators established by genetic methods [2] .
Content
Bacteria
Most bacterial replicons are represented by ring DNA molecules. For example, the majority of bacterial chromosomes and plasmids , as well as the DNA of many bacteriophages, are ring molecules with a single replication origin [3] [4] .
Bacteria can have many replicons: several chromosomes, plasmids, etc. These bacteria include the purple bacterium Rhodobacter sphaeroides , cholera vibrio [5] and Burkholderia multivorans . Their “secondary” or “tertiary” chromosomes are molecules representing a mixture of the true chromosome and plasmids . Such mixed chromosomes are sometimes called chromids . Different species of the genus Azospirillum have 7 replicons, in particular, Azospirillum lipoferum has 1 bacterial chromosome, 5 chromid, and 1 plasmid [6] . Large plasmids of gram-negative bacteria may contain several replicons [7] .
Archaea
Since the archaeal ring chromosomes are similar to the bacterial in structure, it was initially suggested that they in most cases represent a single replicon. The chromosome of the first studied archaeon Pyrococcus abyssi did indeed have a single point of origin of replication. Later it was found that the chromosomes of at least two representatives of the genus Sulfolobus , S. solfataricus and S. acidocaldarius , contain three replication origin points and consist, respectively, of three replicons [8] .
Eukaryotes
Each eukaryotic chromosome has many replicons. The average size of such a replicon is small compared with the prokaryotic: about 40,000 base pairs in yeast and fruit fly and about 100,000 base pairs in other animals . The size of individual replicons within the genome may differ by more than 10 times. Typically, two replication forks are formed at each replication start point, that is, bidirectional replication is performed. Unlike bacterial ones, eukaryotic replicons do not supposedly have replication termination sites. It is more likely that replication forks continue to move until they meet a fork moving towards [3] .
According to reports, eukaryotic replicons are not replicated simultaneously, but in a specific time sequence. It is known that replicons located next to active genes are usually replicated first, and replicons in the heterochromatin region are the last. There is reason to believe that the regulation of replicon activity is regional in nature, that is, groups of replicons located close to each other are activated jointly [3] .
Mitochondria that appear in eukaryotic cells use unidirectional replication with two points of origin of replication.
See also
- Replication start point
Notes
- ↑ Zzaman S., Abhyankar MM, Bastia D. Reconstitution of F factor DNA replication in vitro with purified proteins // J Biol Chem. - 2004. - Vol. 279, No. 17 . - P. 1740410. - PMID 14973139 .
- ↑ Hyrien O., Rappailles A., Guilbaud G., Baker A., Chen CL, Goldar A., Petryk N., Kahli M., Ma E., d'Aubenton-Carafa Y., Audit B., Thermes C ., Arneodo A. From simple bacterial and archaeal replicons to replication N / U-domains // J Mol Biol. - 2013 .-- Vol. 425, No. 23 . - P. 4673-89. - DOI : 10.1016 / j.jmb.2013.09.09.021 . - PMID 24095859 .
- ↑ 1 2 3 Jocelyn Krebs. Chapter 11. The Replicon // Lewin's GENES X. - Jones & Bartlett Learning, 2011 .-- ISBN 0763766321 .
- ↑ Mott ML, Berger JM DNA replication initiation: mechanisms and regulation in bacteria // Nat Rev Microbiol. - 2007. - Vol. 5, No. 5 . - P. 343-54. - PMID 17435790 .
- ↑ Tagomori K., Iida T., Honda T. Comparison of genome structures of vibrios, bacteria possessing two chromosomes // J Bacteriol. - 2002. - Vol. 184, No. 16 . - P. 4351-8. - PMID 12142404 .
- ↑ Wisniewski-Dyé F., Borziak K., Khalsa-Moyers G., Alexandre G., Sukharnikov LO, Wuichet K., Hurst GB, McDonald WH, Robertson JS, 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 AH, González V., Mavingui P ., Zhulin IB Azospirillum genomes reveal transition of bacteria from aquatic to terrestrial environments // PLoS Genet. - 2011. - Vol. 7, No. 12 . - P. e1002430. - DOI : 10.1371 / journal.pgen.1002430 . - PMID 22216014 .
- ↑ Thomas, Christopher M. Horizontal Gene Pool: Bacterial Plasmids and Gene Spread. - 1. - CRC Press, 2000-05-01. - ISBN 9057024624 .
- ↑ Barry ER, Bell SD DNA replication in the archaea // Microbiol Mol Biol Rev. - 2006. - Vol. 70. - Vol. 4 . - P. 876-87. - PMID 17158702 .