Transposable elements are mobile DNA sequences found in all organisms that were first discovered by Barbara McClintock in corn in the 1940s. They make up at least 50% of human DNA and move via "cut and paste" or reverse transcription mechanisms. There are several classes of transposable elements including DNA transposons, LTR retrotransposons, non-LTR retrotransposons, and insertion sequences found in bacteria. Transposable elements move within genomes through the action of the transposase enzyme and can cause mutations when they insert into genes.

2. ANJU S NAIR
SCHOOL OF BIOSCIENCES
MG UNIVERSITY
KOTTAYAM

3. Transposable elements
• Transposable elements are mobile DNA sequences found in the
genomes of all organisms
• Barbara McClintock first discovered transposable elements in corn in
the 1940s
• Also called ‘jumping genes’ or ‘junk DNA’
• They make up at least 50% of human DNA
• Most transposable elements are able to insert at many different
locations, relying on mechanisms that are distinct from homologous
recombination
• Transposable elements are mobile DNA sequences that often cause
mutations

4. • The first TE discovered in bacteria is called
insertion sequences
• IS elements are the simplest transposons
• Short, flanking direct repeats from 3 to 12
bp long are present on both sides of most
transposable elements.
• These sequences are necessary for the DNA
between them to be transposed by a
particular enzyme, transposase

5. DISCOVERY
• Barbara McClintock, a Maize Geneticist discovered
transposons in 1940s
• McClintock hypothesized that certain cells lost genetic
material, while others gained what they had lost
• Published an article "Induction of Instability at
Selected Loci in Maize“ in 1953
• She was awarded a Nobel Prize in Physiology or
Medicine in 1983 for her discovery of TEs

6. TRANSPOSASE
• Transposase is the enzyme that catalyzes the movement of the transposon to
another part of the genome
• It binds to the end of a transposon to facilitate
transposition
• Genes encoding transposases are widespread in the
genomes of most organisms and are the most
abundant genes known

7. CLASSIFICATION
Eukaryotes
DNA
Transposons
Retrotranspo
sons
LTR Non LTR
Prokaryotes
IS Elements Transposons
Composite
Non
Composite

8. DNA Transposons
• Otherwise called Class 2 transposons
• They are mobile DNA that move utilizing a single or double-stranded
DNA intermediate
• DNA fragments transpose directly from DNA segment to DNA
segment, producing a DNA copy that move by cut and paste
mechanism
• Does not involve an RNA intermediate
• Terminal inverted repeats are present
• They can inactivate or alter the gene expression by the insertion
within introns, exons or regulatory regions

10. RETROTRANSPOSONS
• The mobile DNA that move from place to place in a genome by
reverse transcription of an RNA transposition intermediate
• Use reverse transcriptase to make RNA intermediate
• There are two types of retrotransposons distinguished by their DNA
sequence topology and mechanism of transposition
Long Terminal Repeats Retroransposons & Non Long Terminal
Repeats Retrotransposons

11. LTR Retrotransposons
• LTR retrotransposons are generally 5–7 kb long
• They are characterized by having long terminal direct repeats, a few
hundred base pairs long
• Similar to the proviral form of retroviruses, but with a difference in
the protein coding region - lack the ENV protein, so they're stuck in
the cell

12. • Non-LTR retrotransposons typically contain one or two open reading
frames
• Central to retrotransposon mobilization is reverse transcriptase (RT)
activity, and thus all autonomous non-LTR retrotransposons contain
an RT domain.
• The 5' and 3' untranslated regions (UTRs) of non-LTR retrotransposons
are quite variable
Non LTR Retrotransposons

14. Insertion Sequences
• IS elements are the simplest transposable elements and are normal
constituents of bacterial chromosomes and plasmids
• All such elements end with perfect or nearly perfect terminal inverted
repeats (IR’s) of 9 to 41 bp
• Integration of IS elements along the chromosome may cause
mutation by disrupting either the coding sequence of a gene or a
gene’s regulatory sequence
• The presence of IS elements can cause deletion or inversion type of
mutations in the adjacent DNA

16. TRANSPOSNS
• The transposon is more complex mobile genetic element than the IS
element
• The Tn contains gene coding for transposase as well as other proteins
TRANSPOSONS
Composite
Transposons
Non Composite
Transposons

17. COMPOSITE TRANSPOSONS
• These Tn elements may be 1000 bp long and have a complex
structure with a central region containing genes that confer resistance
to antibiotics
• They are flanked by IS elements of same type on both sides called IS-R
and IS-L. Transpositon of these Tn occurs because of the function of
the IS elements they contain

19. NON COMPOSITE TRANSPOSONS
• Non-composite transposons do not contain IS elements at their ends,
but has the repeated sequences at their ends that are required for
transposition
• Like Composite transposons, they also contain genes for drug
resistance
• Eg; Tn3

20. MECHANISM OF TRANSPOSITION
• Transposition is the process in which the mobile DNA is inserted into
a genome
• The mobile elements that transpose through DNA are called
transposons and those via RNA are referred to as retrotransposons
• The process involves the action of transposase and resolvase
transposase acts on each end of the transposons
resolvase acts in duplicatd copies
• There exists mainly 2 mechanisms of transposition; and replicative

21. conservative

22. Replicative

23. RNA Mediated Transposition

24. USES AND FUNCTIONS
• Cause mutations
• Provide substrates for genetic rearrangements
• Agents of genome evolution
• The evolution of Antibiotic resistance carrying microorganisms
• Derivatives of Tn 10 can be used for making insertions in bacterial
chromosome
• Genes can be transferred from one strain to another and can be
cloned easily