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A Review on Transposons and Its Utilization As Genetic Tool Int.J.Curr.Microbiol.App.Sci (2020) 9(2): 1874-1884 International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 9 Number 2 (2020) Journal homepage: http://www.ijcmas.com Review Article https://doi.org/10.20546/ijcmas.2020.902.214 A Review on Transposons and its Utilization as Genetic Tool Sadia Perween, Deepak Kumar* and Anand Kumar Department of Plant Breeding and Genetics, Bihar Agricultural University, Sabour (Bhagalpur), India *Corresponding author ABSTRACT Transposable elements, found in almost all organisms, are short sequences of DNA that have the ability to move from one location to the other locations in the genome. Transposons make up 10% of eukaryotic genomes. They provide a means for genomic change and variation, particularly in response to stress (McClintock’s stress hypothesis).There is no known example of transposon playing a normal role in K e yw or ds development. They are called as selfish DNA and can be used as genetic markers, as mutagens for transposon tagging and isolation of gene, as transformation vectors and as transposons, cloning vehicle. Transposons are potent forces of genetic change and have a significant insertational aspect in the evolution of many genomes. DNA transposons can be used as genetic tools to mutagenesis, introduce a piece of foreign DNA into any genome. They have been utilized for transposon tagging transgenesis and insertional mutagenesis in diverse organisms, as these elements are not Article Info generally dependent on host factors to facilitate their mobility. Thus, DNA transposons are powerful tools to analyze the regulatory genome, study the development of embryo, Accepted: identify genes and pathways involved in disease or pathogenesis of pathogens, and helps in 15 January 2020 gene therapy. Transposons are used for gene cloning since insertion of a transposon into a Available Online: gene upsets its function which develops a visible mutant phenotype. When the DNA 10 February 2020 sequence of the transposon is known, it is possible to clone the disrupted gene by employing the transposable element as a tag to locate the segment of DNA possessing the element. Transposon tagging involves initiating transposition, screening for mutations caused by transposon insertion, discovering the element responsible for the developed mutation, and cloning the tagged gene. Introduction typically in large numbers viz., they make up approximately 50% of the human genome and Transposable elements (jumping genes, up to 90% of the maize genome (SanMiguel, insertion sequences or mobile DNA elements) 1996). are short sequences of DNA that can move from one location to the other in the genome, Types of transposons often making duplicate copies of them in the process. They are found in almost all There are the transposable elements that need organisms (both prokaryotes and eukaryotes), reverse transcription (i.e., the transcription of 1874 Int.J.Curr.Microbiol.App.Sci (2020) 9(2): 1874-1884 RNA into DNA) to transpose, called Conservative and replicative transposition retrotransposons or class 1 TEs, whereas, some elements do not have such requirement In conservative transposition, the sequence is for transposition and are known as DNA excised from its original position and transposons or class 2 TEs. reinserted elsewhere without increasing its copy number, whereas, in replicative DNA transposons transposition transposons creates a copy of itself and the copy is inserted at a new The complete or "autonomous" class 2 TEs position. encodes the protein transposase, required for insertion and excision. A few of these TEs Bacterial transposons also encode other proteins. Its mobility is always on its own (insertion or excision), Most transposons in bacteria transpose as from the genome by means of "cut and paste" DNA. On the other hand, in eukaryotes they mechanism. are mostly retrotransposons. Short direct repeats are created at the site of insertion Retro transposons flanking the mobile element. Class 2 elements, known as retrotransposons, 1. IS Element: it constitutes inverted move by the action of RNA intermediaries. repeat at each end of insertion i.e. they do not encode transposase; rather, sequence and between the inverted they produce RNA transcript followed by repeats is a protein coding region action of reverse transcriptase enzymes to encoding enzymes required for reverse transcribe the RNA sequences back transposition. Short direct repeats are into DNA, which is to be inserted into the adjacent to both ends of the inserted target site. element. 2. Composite transposons: they are Autonomous and nonautonomous larger than IS elements containing transposons protein coding region along with those required for transposition and usually The class 1 and class 2 TEs can be either carry genes for antibiotic resistance. autonomous or non autonomous. Autonomous 3. Non composite transposons: they TEs have their own mobility, while non terminate with IS element but contain autonomous elements require the presence of terminal inverted repeats. other TEs to move from one place to another in genome. The reason behind it is that non Transposable elements in eukaryotes autonomous elements lack the gene for the transposase or reverse transcriptase that is Transposons constitute 10% of eukaryotic required for their transposition, so they need genomes being similar in structure to bacterial these proteins from another element in order IS elements with retroransposons being much to move along the genome. more profuse. For example Ac elements are autonomous and Element 1 - Yeast ty elements: can move on their own, whereas, Ds elements are non autonomous and require the presence The yeast has approximately 35 copies of a of Ac in order to transpose. transposable element called as Ty in its haploid genome. 1875 Int.J.Curr.Microbiol.App.Sci (2020) 9(2): 1874-1884 Element 2 - Drosophila transposons: mutations are stable only if Ds are present; whereas unstable in the presence of an Ac Drosophila transposons consists of retrovirus element. like elements i.e. retro transposons and are 5000 to 15,000 nucleotide pair long. Ds is immobile in the absence of Ac and remains as a stable insertion in the Element 3 - Controlling elements in maize: chromosome. In the presence of an Ac Mcclintock’s experiments: the ds element: element, it gets activated, causing it to transpose to a new site or to break the In the 1950s, Barbara McClintock studying chromosome in which it is located. corn kernels found that, rather than being purple or white; they had spots of purple Biological significance of transposons pigment on normally white kernels. The genetic and cytological studies concluded that Transposons are a means for genomic change the spotted phenotype was not the result of and variation, especially in response to stress any conventional kind of mutation but due to (McClintock’s stress hypothesis). There is no a controlling element, which is now known as known example of an element playing a a transposon. normal role in development, hence called as selfish DNA. The spotted kernelis the result of wild type C and c (colorless) gene. The presence of C Application of transposons gene makes the kernel purple, c (colorless) mutations block purple pigment production, Transposons as genetic markers (Izsvak and so the kernel is colorless. During kernel Ivics, 2004)- as it changes the pattern of development, mutation reverts, due to which restriction fragment analysis there is a spot of purple pigment. The genetic Transposons as mutagens and transposon nature of the reversion is approved by the fact tagging (Whitham et al., 1994 Dinesh et that descendants of the cell which had the al., 1995) for isolation of gene reversion also can give rise to pigmentation. Transposons as transformation vectors The sooner in development the reversion Transposons as cloning vehicle occurs, the larger is the purple spot. McClintock determined that the original c Transposons are powerful forces of genetic (colorless) mutation is the resultant of a change and have a significant role in the mobile controlling element, a genetic factor evolution of many genomes. As genetic tools, known as Ds (Dissociation), which gets DNA transposons can be utilized to insert a inserted into the C gene. The action of piece of foreign DNA into a genome. They Dsrelies on the presence of an unlinked gene, have been aided for transgenesis and Ac (Activator). insertional mutagenesis inorganisms, as these elements are not generally dependent on host Ac is needed for transposition of Ds into the factors for their mobility. Thus, DNA gene. It can also move the Ds out of the C transposons are useful devises for analyzing gene, giving rise to the wild type revertant, the regulatory genome, study embryonic i.e., a purple spot. Ac is the autonomous development, identifying genes and pathways element, and therefore, mutations caused by related to disease or pathogenesis of Ac are unstable. In contrast, Ds is the non- pathogens, and contributing to gene therapy. autonomous element of the family. The Ds 1876 Int.J.Curr.Microbiol.App.Sci (2020) 9(2): 1874-1884 Transposon tagging created by merging the two types of elements, the transposase source can be segregated. As Transposons are used for gene cloning as a result, the new insertions are stabilized and insertion of a transposon into a gene disarms thus any mutant phenotypes generated gets its function, producing an observable mutant stabilized. Transposase can be reintroduced phenotype. When the DNA sequence of the later for remobilizing the element to reverse transposon is known, it is likely to clone the the mutant phenotype or to produce new disrupted gene by using the transposable alleles of the tagged gene. element as a tag to identify the segment of DNA containing the element. Transposon Obtaining the Sequence of the transposon tagging includes inducing transposition, tag screening for mutations caused by insertion, recognizing the element responsible for Transposon as a molecular tag for gene mutation, and finally cloning the tagged gene.
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