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Retrotransposons also called Class I transposable elements or transposons via RNA intermediates are genetic elements that can amplify themselves in a genome and are ubiquitous components of the DNA of many eukaryotic organisms. These DNA sequences use a "copy-and-paste" mechanism, Lines - Lines I they are first transcribed into RNAthen converted back into identical DNA sequences using reverse transcriptionand these sequences are then inserted into the genome at target sites.
Retrotransposons form one of the two subclasses of transposonswhere the others are DNA transposonswhich does not involve an RNA intermediate. Retrotransposons are particularly abundant in plants, where they are often a principal component of nuclear DNA. The retrotransposons' replicative mode of transposition by means of an RNA intermediate rapidly increases the copy numbers of elements and thereby can increase genome size. Like DNA transposable elements class II transposonsretrotransposons can induce mutations Lines - Lines I inserting near or within genes.
Furthermore, retrotransposon-induced mutations are relatively stable, because the sequence at the insertion site is retained as they transpose via the replication mechanism. The Happier - Jennifer Trynin - Happier step of Lines - Lines I DNA may be carried out by a reverse transcriptasewhich the retrotransposon encodes. The understanding of how retrotransposons and their hosts' genomes have co-evolved mechanisms to regulate transposition, insertion specificities, and mutational outcomes in order to optimize each other's survival is still in its infancy.
Retrotransposons, also known as class I transposable elementsconsist of two subclasses, the long terminal repeat LTR-retrotransposons and the non-LTR retrotransposons. LTR retrotransposons are further sub-classified into the Ty1- copia -like PseudoviridaeTy3- gypsy -like Metaviridaeand BEL-Pao-like groups based on both their degree of sequence similarity and the order of encoded gene products.
Ty1- copia and Ty3- gypsy groups of retrotransposons are commonly found in high copy number up to a few million copies per haploid nucleus in animals, fungi, protista, and plants genomes. BEL-Pao Lines - Lines I elements have so far only been found in animals. Although retroviruses are often classified separately, they share many features with LTR retrotransposons.
A major difference with Ty1- copia and Ty3- gypsy retrotransposons is that retroviruses have an envelope protein ENV. A retrovirus can be transformed into an LTR retrotransposon through inactivation or deletion of the domains that enable extracellular mobility. If such a retrovirus infects and subsequently inserts itself in the genome in germ line cells, it may become transmitted vertically and become an Endogenous Retrovirus ERV. In plant genomes, LTR retrotransposons are the major repetitive sequence class, e.
They can also be found in high copy numbers, as shown in the plant species. These functions include reverse transcriptase and endonuclease activities, in addition to a nucleic acid-binding property needed to form a ribonucleoprotein particle. It is shown to be transcribed and endogenous proteins are observed. RNase H as well as a reverse transcriptase. Elements in the R2 group have REL Lines - Lines I endonuclease, which shows site specificity in insertion.
LTR retrotransposons and SINEs move by copying themselves instead of moving by a cut and paste like mechanism, as class II transposons dothey enlarge the genome.
SINEs are the only TEs that are non-autonomous by nature, meaning that they did not evolve from autonomous elements. They are small bases  and rely in trans on functional LINEs for their replication, but their evolutionary origin is very distinct. SINEs are postulated to originate from the IV Marcha Oriental - Alicia De Larrocha, Granados* - Seis Piezas Sobre Cantos Populares Españoles, E retrotransposition of various RNA pol III transcripts, and have appeared separately numerous times in evolution history.
SINEs do not encode a functional reverse transcriptase protein and rely on other Sanford & Son Theme -Nbc-Tv (The Streetbeater) - Quincy Jones - Youve Got It Bad Girl elements for the transposition, especially LINEs . Alu and B1 elements, with their 1.
Alu elements are approximately base pairs long, do not contain any coding sequences, and can be recognized by the restriction enzyme AluI hence the name.
The distribution of these elements has been implicated in some genetic diseases and cancers. Hominid genomes contain also original elements termed SVA. They are composite transposons formed by the fusion of a SINE-R and an Alu, separated by a variable number of tandems repeats.
Less than 3kb in length and apparently mobilized using LINE1 machinery, they are around copies in human or gorilla genomes, and less than in orangutan. SVA are one of the youngest transposable element in great apes genome and among the most active and polymorphic in the human population.
From Wikipedia, the free encyclopedia. Main article: LTR retrotransposon. Main article: Endogenous retrovirus. Main article: Long interspersed nuclear element.
Main article: Short interspersed nuclear element. Annals of Botany. The Plant Journal. February Molecular and Cellular Biology. BMC Evolutionary Biology. Nature Reviews. Genome Biology. PLoS Genetics. Plant Molecular Biology. BMC Genomics. Cytogenetic and Genome Research. Genome Research. Introduction to genetic analysis 9th ed. New York: W. Bickmore WA White Dope - 2 Tell - Ten Years. A dictionary of genetics 5th ed.
Oxford [Oxfordshire]: Oxford University Press. International Review of Cytology. Nature Genetics. Science Advances. Genetics : repeated sequence. Alu sequence MIR. Pathogenicity island symbiosis island.