transposon, class of genetic elements that can “jump” to different locations within a genome. Although these elements are frequently called “jumping genes,” they are always maintained in an integrated site in the genome. In addition, most transposons eventually become inactive and no longer move.1

1. Dr. Rachana Choudhary
Department of Microbiology
Shri Shankaracharya Mahavidyalaya, Junwani, Bhilai

2. SYNOPSIS
Introducton
Discovery Of Transposons
Types Of Transposonson
-DNA Transposons
- Retrotransposons
Bacterial Transposons
-Insertion Sequence
-Composite Transposons
-Tn-type Transposons
Mechanism of Transposition
1.Replicative
2.Non Replicative
Disease Caused by Transposition
Application
Conclusion
Reference

3. INTRODUCTION
Transposon, class of genetic elements that can “jump” to different locations
within a genome. Although these elements are frequently called jumping
genes, Transposable elements , Mobile DNA and are always maintained
in an integrated site in the genome. In addition, most transposons
eventually become inactive and no longer move.
able to move from one place to another within a cell’s genome
sometimes a copy is made and the copy Moves
insertion requires target DNA sequences

4. • In this process, it may
- Cause Mutations.
- Increase (Or Decrease) The Amount of DNA in The Genome.
- Promote Genome Rearrangements.
- Regulate Gene Expression.
- Induce Chromosome
•Breakage and Rearrangement.

5. Discovery of transposons
 Barbara McClintock 1950’s Ac Ds system in maize
influencing kernel color unstable elements changing map
position promote chromosomal breaks.
 Rediscovery of bacterial insertion sequences source of
polar mutations discrete change in physical length of
DNA inverted repeat ends: form “lollipops” in EM after
denaturation.
These mobile segments of DNA are
sometimes called "jumping genes“

6. TYPES OF TRANSPOSONS
There are two distinct types of transposons:
1) DNA transposons
transposons consisting only of DNA that moves directly
from place to place
2) Retrotransposons
- 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

7. Classification of Transposons into two classes
In both cases ds
DNA intermediate
is integrated into
the target site in
DNA to complete
movement
In both cases ds
DNA
intermediate
is integrated into
the target site in
DNA to complete
Movement.

8. BACTERIAL TRANSPOSONS
•In bacteria, transposons can jump from chromosomal DNA
to plasmid DNA and back.
•Transposons in bacteria usually carry an additional gene
for function other than transposition often for antibiotic
resistance.
•Bacterial transposons of this type belong to the Tn family.
When the transposable elements lack additional genes,
they are known as insertion sequences.

9. TYPES of BACTERIAL TRANSPOSONS
1.Insertion sequence
2.Composite transposon
3.Tn3-type transposon

10. 1.Insertion Sequences
•Insertion sequences – IS1 and IS186, present in the 50-kb
segment of the E.coli DNA, are examples of DNA
transposons. Single E. coli genome may contain 20 of them.
•Most of the sequence is taken by one or two genes for
transposase enzyme that catalyses transposition.
•IS elements transpose either replicatively or conservatively.
•Study of E. coli mutations resulting from insertion of 1-2 kb
long sequence in the middle of certain genes.
•Inserted stretches or insertion sequences – could be
visualized by EM.
•IS - molecular parasites in bacterial cells.
•Transposition of IS is very rare – one in 105-107 cells per
generation. Higher rates result in greater mutation rates.

11. Bacterial IS element
• Central region encodes for one or two enzymes required for
transposition. It is flanked by inverted repeats of characteristic
sequence.
• The 5’ and 3’ short direct repeats are generated from the target-site
DNA during the insertion of mobile element.
• The length of these repeats is constant for a given IS element, but
their sequence depends upon the site of insertion and is not
characteristic for the IS element.Arrows indicate orientation

12. Insertion sequences in E.coli
Elements Size (bp) No. of.Copies/Genome
IS1 768 8
IS2 1327 5
IS3 1300 1 or more
IS4 1426 1 or more

14. 2.Composite transposons
•Bacteria contain composite mobile genetic elements that are
larger than IS elements and contain 1 or more protein-coding
genes in addition to those required for transposition:
•Composite transposons - are basically the pair of IS
elements flanking a segment of DNA usually containing one
or more genes, often coding for Antibiotic resistance.
•They use conservative method of transposition.

15. 2.Composite transposon
- Antibiotic resistant gene
- Flank by IS element
(inverted or directed repeat)
- Terminal IS can transpose by in self
Ex. Tn5, Tn9, Tn10

17. 3. Tn3 transposon family
• 5000 bp
• Code for Transposase, β-lactamase, Resolvase
• Function of resolvase decrease Transposase
production Catalyze the recombination of
transposon

20. Mechanism of transposition
Two distinct mechanisms of transposition:
1.Replicative transposition – direct interaction between the
donor transposon and the target site, resulting in copying of
the donor element
2.Conservative transposition – involving excision of the
element and reintegration at a new site.

21. 1. Replicative transposition
Copy of transposon sequence
Transposase enzyme cut target DNA
Transposition
Duplication of target sequence

22. Replicative transposition

23. 2. Non-replicative (conservative)
transposition
- Cannot copy transposon sequence
-Transposition by cut and paste model
Cut transposon sequence from donor molecule
attach to target site
Ex. IS10, Tn10

24. Non-replicative (conservative) transposition

25. Mechanism of transposition

26. Transposons causing diseases
Transposons are mutagens. They can damage the genome of their host
cell in different ways:
1. A transposon or a retrotronsposon that inserts itself into a functional
gene will most likely disable that gene.
2. After a transposon leaves a gene, the resulting gap will probably not
be repaired correctly.
3. Multiple copies of the same sequence, such as Alu sequences can
hinder precise chromosomal pairing during mitosis and meiosis,
resulting in unequal crossovers, one of the main reasons for
chromosome duplication.

27. Diseases caused by transposons include
-Hemophilia A and B
-Severe combined immunodeficiency
-Porphyria
-Cancer
-Duchenne muscular dystrophy

28. Applications
• The first transposon was discovered in the plant maize
(Zea mays, corn species), and is named dissociator (Ds).
Likewise, the first transposon to be molecularly isolated
was from a plant (Snapdragon).
• Transposons have been an especially useful tool in plant
molecular biology.
• Researchers use transposons as a means of mutagenesis.
• To identifying the mutant allele.
• To study the chemical mutagenesis methods.
• To study gene expression.
• Transposons are also a widely used tool for mutagenesis of
most experimentally tractable organisms.

29. CONCLUSION
• The genomes of nearly all organisms contain mobile genetic
elements that can move from one position in the genome to another
by either transposons or conservative Site-specifc combination
processes.
• In most cases this movement is random and happens at a very low
frequency.
• Mobile genetic elements include transposons, which move within a
single cell (and its descendants) plus those viruses whose genomes
can integrate into the genomes of their host cells.
• A common feature of all mobile elements is the presence of short
direct repeats flanking the sequence.
• Mobile DNA elements that transpose to new sites directly as DNA
are called DNA transposons; those that first are transcribed into an
RNA copy of the element, which is then reverse-transcribed into
DNA, are called retrotransposons.

30. REFERENCE
•Microbiology by Dubey & Maheshwari
•Biotechnology by R.C. Dubey
•Molecular Cell Biology Lodish, 5th edition
•Molecular Biology of the cell Alberts, 5th edition

31. THANK YOU