transposition 97

8/6/2019 Transposition 97

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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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transposition 97

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