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Transposition
Presented by:Pradeep Kumar
CIFE- Mumbai.
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Introduction
Transoposon are DNA element that can hop or
transpose from one place to another and first
discovered by Barbra Mc Clinteck in 1950 in
corn and about 20 year later in bacteria.
It exist in all organism on earth e.g in human
almost half of an DNA may be transposons.
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Transposition
Movement by a transposon is called transpositionand carried out by an enzyme called transposasesand it is encoded by transposons itself so that it is
called jumping gene. In one sentence:- the netresult of transposition is that the transposonappears at a place in DNA different from where itwas originally
but all DNA movenment is not calledtransposition such as homing DNA element &Retrotransposons
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Role of transposon
Offer a way of introducing genes from one
bacterium into the chromosome of anopther
bacterium to which it has little DNA sequence
homology.
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Way of transferring transposons
Can be cut out of one DNA and then inserted intoanother DNA or can be copied and then insertedelsewhere. It is achieved by transposase enzyme
that cuts the donar DNA at the ends oftransposons and then insert the transposons intothe target DNA.
It is highly regulated and occur only rarerly
Frequency of transposition :- about once in every10 cell division to about once in every 10 celldivision.
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Structure of bacterial transposon
Many different type of bact. Transposons are there ,some are smaller of about 1000 bp long and carry onlythe genes for transposases that prometer themovement in DNA where as larger transposon maycontain one or more other genes such as those whichis resistant to Ab.
All bact. Transposons contains repeats at their end,which are usually inverted repeat(fig 9.2) and also
presence of short direct repeats of target DNA thatbracket the transposons & during insertion oftransposons , this sequence duplicated.
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Types of bact. transposons
1. Insertion seqence element:- smallesttransposons having 750 to 2000 bp length andencode little more than transposase enzyme
that promote their transposition . They didntcarry selectable genes and discovered onlybecause they inactivate a gene if they happen tohop into it and causing a detectable phenotype
change. There are around 700 IS element foundin bact. And in plasmid also found which areimp. for formation of Hfr strains.
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Conti
2. Composite transposons :- when two
transposons of the same types form a larger
transposons called a composite transposons,
by brackating other genes.
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Types of transposition
1. Outside End transposition :- this is for
transposition of a composite transposons .
Here each IS element can transpose
independently as the transposase acts on
both of its end.
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Conti..
Inside end transposition:- the transposase
encoded by one IS element in a composite
transposons can also act on the inside end
of both IS element i.e. two ends that are
closest to each other. After inside end
transposition there may be chance of creation
of a new composite transposons .
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Conti.
3. Non composite transposition
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How to assay transposition
1. By observing phenotypic expression
2. Suicide vector
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3. Mating out assay for transposition
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Molecular model for transposition
1. Replicative
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Replicative
transposition
1. transposase
Note: the cuts areon differentstrands
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Replicative
transposition
2. Ligation to target ends
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Replicative
transposition
3. 3-ends prime replication
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Replicative
transposition
4. Formation of co-integrate
and resolution (resolvaseTnpR)
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2. Cut and paste or conservative mechanism
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Relationship between replicative and
Cut and paste transposition
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Target site specificity
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Regulation of transposition
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Thank U