This presentation provides an overview of What is a transposon,different types of transposons, their mechanism of action, examples for each type of transposons, changes caused due to insertion of transposon into the target gene and applications of Transposons. They are controlling factors in gene expression. Jumping genes is a special area of interest in Genetic research.

1. TRANSPOSABLE ELEMENTS

2. INTRODUCTION
 Transposable elements or transposons are DNA elements capable of
moving ("transposing") about the genome.
 1st transposable element was discovered by Barbara McClintock in maize
in 1950.
 They are “specific” sequence of DNA present in ~40% of the genomic
DNA.
 They are found in the genomes of many kinds of organisms.
 They are also called controlling elements as they affect gene expression.
1983 Nobel Prize in
Physiology and Medicine

3. Two Categories

4. “cut-and-paste” “copy-and-paste”

5. Insertion sequence (IS) elements
1. Simplest type of transposable element found in bacteria.
2. Encode transposase gene for mobilization and insertion.
3. 768 bp to 5 kb.
4. IS1 first identified in E. coli’s galactose operon.
5. Ends of all known IS elements show inverted terminal repeats (ITRs).

6. Integration of IS element in chromosomal DNA.

7. Integration of an IS element may:
• Disrupt coding sequences or regulatory regions.
• Alter expression of nearby genes.
• Cause deletions and inversions in adjacent DNA.
• Result in crossing-over.

8. Transposons
 Similar to IS elements but are more complex structurally and carry
additional genes.
 2 types :
 Composite transposons
 Non composite transposons

9. Composite transposons (Tn):
• Carry genes (example might be a gene for antibiotic resistance) flanked on both
sides by IS elements.
• Tn10 is 9.3 kb and includes 6.5 kb of central DNA (includes a gene for
tetracycline resistance) and 1.4 kb inverted IS elements.
• IS elements supply transposase and ITR recognition signals.

10. Non-composite transposons (Tn):
• Carry genes (example might be a gene for antibiotic resistance) but do not terminate
with IS elements.
• Tn3 is 5 kb with 38-bp ITRs and includes 3 genes; bla (-lactamase), tnpA
(transposase), and tnpB (resolvase, which functions in recombination).

11. P element
 P element of Drosophila melanogaster codes for transposase and repressor of
transposition.

12.  They are genetic elements that can amplify themselves in a genome and are ubiquitous
components of the DNA of many eukaryotic organisms.
 Around 42% of the human genome is made up of retrotransposons
 Retrotransposons : 2 types-
 LTR retrotransposons and
 non-LTR retrotransposons (or retroposons)
 Classification into these subclasses is based on the presence/absence of long terminal
repeats
Retrotransposons

13. Retrovirus-based Transposition

15. LTR retrotransposons
 LTR retrotransposons range from ~100 bp to 11 kb in size.
 LTR retrotransposons are further sub-classified into the
Ty1-copia-like (Pseudoviridae),
Ty3-gypsy-like (Metaviridae) and
BEL-Pao-like groups
 Ty1-copia and Ty3-gypsy groups of retrotransposons are commonly found in high copy number in
animals, fungi and plants genomes.
 BEL-Pao like elements have so far only been found in animals.

16. • May activate or repress target genes, cause chromosome mutations, and
disrupt genes.
Two types:
• Autonomous elements: transpose themselves; possess transposition
gene.
• Non autonomous elements: do not transpose themselves; lack
transposition gene and rely on presence of another Tn
Plant Transposons

18. Non-LTR retrotransposons
1. Long interspersed nuclear elements (LINEs) :
LINEs possess two ORFs, which encode all the functions needed for retro transposition.
Eg : L1 element
 6 kb in human
 Account for 21% of the genome
 ORF 1 is 1 kb length and encodes RNA binding protein.
 ORF 2 is 4kb and encodes bifunctional protein with reverse transcriptase and endonuclease
activity.
 Some cases of hemophilia are known to result newly transposed L1 insertions.

19. 2. SINEs (short-interspersed nuclear sequences) :
SINEs opt the LINE machinery and function as non-autonomous
retroelements.
Eg : Alu element
 ~300 bp long
 account for 13% of the genome
 Dimeric structure with 2 non- equivalent monomers
 Right arm has 31 nucleotide insertion
 Left and right arm are separated by Mid A rich region.
 Left arm contains functional but weak A and B box of RNA
polymerase III internal promotor

20. Alu has inserted in NF-1 gene
Neurofibromatosis: autosomal dominant
Growth of nodules mainly affecting nerves in the skin

21. Applications
 to find mutations in the essential genes
 to transfer the mutation into a new strain
 used to determine whether genes are in an operon.
 genetic mapping
 used to construct operon or gene fusions