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Transposons

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Salim Yassine

on 21 May 2014

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Transcript of Transposons

Transposons
Transposons are segments of DNA that can move around to different positions in the genome of a single cell
Also called Jumping Genes, since they are segments of DNA that can move around to different positions in the genome of a single cell.
May Cause mutations or change the amount of DNA in the Cell.
There are two types: Class 1 transposons and Class 2 transposons
Most on transposons result in silent mutations
What are Transposons ?
Background
Transposons were first discovered by Barbara McClintock in the 1940’s, when she was studying maize, aka “Indian corn.”
McClintock saw that the corn kernels, which are somatic cells, would have a mutation that changes the color of its kernels, and this random color pattern would be seen on the descendants
She figured out that transposons are responsible for translocation, insertion and deletion.
Classes:
Class 2 tranposons is just DNA that moves directly from place to place.
Class 2
They are first taken out of its location and then inserted into a new location.
This process requires Transposase, which is usually encoded in the transposons.
Transposase binds to both ends of the transposon, and then transfer it into a sequence of DNA that makes up the target site. Not all transposons need a specific target site, which means that most can just insert themselves anywhere.
After the transposon is inserted to the host DNA, any gaps produced would be filled in according to Watson-Cricks base pairing.
Often transposons lose their gene for transposase. But as long as somewhere in the cell there is a transposon that can synthesize the enzyme, their inverted repeats are recognized and they, too, can be moved to a new location.
Inverted repeats are usually found at both ends of the transposon and are identical sequences reading in opposite directions.
Bacteria
They are first taken out of its location and then inserted into a new location.
This process requires Transposase, which is usually encoded in the transposons.
Transposase binds to both ends of the transposon, and then transfer it into a sequence of DNA that makes up the target site. Not all transposons need a specific target site, which means that most can just insert themselves anywhere.
After the transposon is inserted to the host DNA, any gaps produced would be filled in according to Watson-Cricks base pairing.
Often transposons lose their gene for transposase. But as long as somewhere in the cell there is a transposon that can synthesize the enzyme, their inverted repeats are recognized and they, too, can be moved to a new location.
Inverted repeats are usually found at both ends of the transposon and are identical sequences reading in opposite directions.
Also known as MITE, is almost identical sequences of about 400 base pairs flanked by inverted repeats about 15 base pairs long.
Since these are too small to code for proteins, it is believed that they are larger transposons that do the encoding
Miniature Inverted-repeat Transposable Elements
Class 1
These are known as retrotransposons.
They move within a genome by either "copy-and-paste" (which leaves copy in the original site) or "cut-and-paste" mechanism.
These transposons are made of RNA and then transcribed back into DNA using reverse transciptase, just like a retrovirus.
Human retroviruses behave like retrotransposons because they contain a gene for reverse transcriptase and integrase, which serves the same purpose as transposase in DNA transposons.
Future Applications
Transposons are an explanation for changes and variations in genome, especially in response to stress.
Evidence shows that transposable elements played a role in eukaryotic evolution; they are considered genomic parasites who rearrange to create novelty and benefit its host.
They can also be useful in genetic engineering. Certain genes can be activated by inserting transposons.
Biological Importance
Drawbacks
The Sleeping Beauty Transposon System
The insertion of the transposon may disrupt a gene, mutate it, and it usually inactivates it.
The transposon might jump again, which returns the gene back to normal, but it usually stays would put and permanently inactivates it.
The SB transposon, along with its transposase, was synthetically coined to introduce precise DNA sequences into chromosomes of vertabrates using the cut-and-paste mechanism.
Whit the SBTS, new traits can be introduced and new genes can be discovered along with their functions.
The SBTS consists of:
The SB Transposon
The SB Transposase
A Therapeutic gene
ADVANTAGES
• Non-viral — avoids immunologic reactions associated with viral vectors.
• Insulated — proprietary transposon designed to avoid activation of non-target genes.
• Life-long therapy — more reliable and sustainable results compared to viral vectors.
• Applicable in a broader range of diseases than viral vectors — ability to accommodate genes of many sizes.
• Highest activity — of any transposon system used in human cells.
The Sleeping Beauty transposon carrying the therapeutic gene is "cut" out of the plasmid vector by the engine of this machine (the transposase) and then "pasted" directly into the chromosome. The operation of this biological nano machine is unique and proprietary to DGI
Non-viral vectors are easier to engineer and manufacture.
Transposable elements are non-viral gene delivery vehicles found everywhere in nature. Transposon-based vectors have the capacity of stable genomic integration and long-lasting expression of transgene constructs in cells.
A way the Sleeping Beauty Transposon is used today is to discover cancer-causing genes by insertional mutegenesis (the transposon inserted "knocksout", or disrupts, the gene.) This process is used to create knockout mice.
However, the most exciting application for the transposon is gene therapy.
Trans
posons Are Genetic E
vidence of Evolution
Types of Class 1
LTRs
Non-LTRs
long terminal repeats on both ends
lacks long repeats
Short Interspersed Elements
Also known as SINEs
They are relatively short DNA sequences (100-400 base pairs) that represent molecules made from RNA polymerase III
The most abundant SINEs are Alu elements, and they happen to be the most abundant mobile elements in the human genome.
Long interspersed elements
Also known as LINEs
Most of these belong to a family called LINE-1 (L1).
These L1 elements are DNA sequences that range in length from a few hundred to as many as 9,000 base pairs.
Only about 50 L1 elements are functional "genes"; that is, can be transcribed and translated.
The functional L1 elements are about 6,500 bp in length and encode three proteins, including
an endonuclease that cuts DNA and a
reverse transcriptase that makes a DNA copy of an RNA transcript.
LINEs use the "copy and paste" method, which will increase the number of LINEs in the genome.
The diversity of LINEs between humans helps as markers for DNA fingerprinting.
LTR retrotransposons and DNA transposons in the human genome are not capable of jumping
The only function of transposons are to insert copies of themselves elsewhere in a genome.
The two most well known sequences are SINEs and LINEs.
They account for 30% of a sequence of a genome and are useless (some cause significant damage to genome).
The only way transposons can move from organism to organism is through DNA duplication and inheritance.
When an exact sequence is found in the same location in two different organism, it is direct evidence of a common ancestor.
Example: Three different identical SINE sequences are found in the same genome location of whales and hippos (which are closely realted), while cammels and pigs do not have the same sequence.
Works Cited
"Transposons: Mobile DNA." [Online] Available <http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Transposons.html#Retrotransposons>, 5 December 2011; 27 January 2012.
Pray, Leslie A. PhD. "Transposons: The Jumping Genes." [Online] Available<http://www.nature.com/scitable/topicpage/transposons-the-jumping-genes-518>. 2008; 28 January 2012.
Largaespada, David A. "Generating and manipulating transgenic animals using transposable elements." [Online] Available <http://www.ncbi.nlm.nih.gov/pmc/ articles/PMC280724/>. 7 November 2003; 30 January 2012.
"Gene Delivery Technology." [Online] Available<http://www.discoverygenomics.net/sbts.html>; 29 January 2012.
Bowen Nathan J. and Jordan I. King. "Transposable Elements and the Evolution of Eukaryotiv Complexity." [Online] Available<http://www.horizonpress.com/cimb/v/v4/07.pdf>. 2002; 28 January 2012.
Class 1 Transposons are retrotransposons that first transcribe the DNA into RNA and then use reverse transcriptase to make a DNA copy of the RNA to insert in a new location.
Thank you .
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