transposable elements

1. Group 5
SUBMITTED TO : DR Tayyaba Shaheen
SUBMITTED BY : Hifza Shahid
Ghulam Fatima
Mehak Fatima
Misha Miraj
COURSE TITLE : Advance in Cell
MS BIOTECHNOLOGY(SEMESTER 1)

2. Transposable Element

3. Outline
 Definition
 History
 Characteristics of transposable elements
 Mechanism of transposition
 I. Replicative transposition or copy paste transposition
 Example
 II. Conservative or non-replicative: cut and paste transposition
 III. Retro-transposons
 On the basis of the Organisms in which they are present
 Transposons in Prokaryotes
 Transposons in Eukaryotes
 P Elements
 Transposons in Human
 Applications
 Effects

4. Definition's
 Transposable elements are DNA sequence that move from one location in a chromosomes
to another within the same chromosomes or into another chromosomes.
 A transposable elements is a DNA sequence that can change its position within a genome.
 These are also known as” jumping genes”.
 Transposable elements (both active and non-active) occupy approximately half the human
genome.
 Transposition results on duplication of genetic material.

6. History
BarbaraMcClintok
 Transposable elements(TE) are 1st
Discovered by Barbara McClintok
in corn (maize) in 1940.
 She found genetic elements regularly jump
to new location affecting the gene expression.
Maize kernels show variation in colour.
Later in 1960s Bacteria & Bacteriophage were
shown to possess Transposable elements (TE).

7. Characteristics of transposable elements
 Transposable elements are specific sequence of DNA that codes for enzymes for their
transposition from one position to another position in the chromosome.
 Transposable elements undergoes both replication and recombination process. However,
they lacks the site for origin of replication. So, they have to depend upon host DNA or
plasmid for their replication.
 All transposable elements are commonly known as transposons or mobile gene or jumping
genes that changes their location and insert into different location in a chromosome or into
other chromosome.
 Transposable elements contributes to the repetitive sequences in the genome of the
organisms. Human genome contains 50% repetitive sequences.

8. Mechanism of transposition:
 There are different type of transposable elements depending upon structure and
mechanism. On this basis, there are three different mechanism of transposition
(Replicative, conservative and Retro-transposition). Most prokaryotes and eukaryotes
employed one of two-either replicative or conservative mechanism of transposition
whereas retro-transposition is only employed by eukaryotes.
 Three types:
 Replicative transposition
 Conservative or non-replicative transposition
 Retro-transposition

9. I. Replicative transposition or copy paste
transposition:
 Replicative transposons are those transposons which at first replicates itself and then insert
one copy of it into new position. Therefore, during replicative transposition, the
transposable elements is replicated and one copy is inserted into new position while one
copy remains at original position.
 This transposition is catalyzed by an enzyme transposase which is encoded by the
transposable element itself.
 It is also known as copy and paste transposition.
 Replicative transposition is present only in prokaryotic organisms.

10. Example:
 Non-composite transposons (Tn3) is a replicative transposons that undergoes transposition
in two stage process. In the first stage, two plasmid- (one containing Tn3 transposons;
donor plasmid) and the other recipient plasmid undergoes fusion catalyzed by transposase
enzymes giving rise to a structure called cointegrate.
 During the formation cointegrate, Tn3 is replicated, and one copy is inserted at each point
where the two plasmids have fused. In the second stage of transposition, the tnpR-encoded
enzyme resolvase which mediates a site-specific recombination between the two Tn3
copies at the resolution site, and when it is completed, cointegrate is resolved into its two
constituent plasmids, each with a copy of Tn3.

12. II. Conservative or non-replicative: cut and
paste transposition
 The conservative transposons are those which changes position by excision from one
position and then insertion into another position within a chromosomes. Therefore, during
conservative transposition, the transposable element is physically cut from its original
position and paste into another position in a chromosome.
 It is also known as cut and paste transposition
 This types of transposition is catalyzed by an enzyme called transposase which is coded by
such transposable element itself.
 Conservative transposition is present in both prokaryotic and eukaryotic organisms

13. III. Retro-transposons:
 The retro-transposons are those transposons, whose RNA is reversed transcribed by reverse
transcriptase enzyme into DNA and the synthesized DNA is inserted into new position in a
chromosome.
 The mechanism of such transposition is known as retro-transposition
 Some of these retro-transposons are related to retro viruses and utilized their reverse
transcriptase enzyme for transposition, such transposable elements are known
as retroposons.
 Retro-transposons are only present in Eukaryotic organisms.

15. On the basis of the Organisms in
which they are present.

16.  1. Transposons in Prokaryotes
 a) Insertion Sequences or IS Elements
 b) Prokaryotic Transposon Element

17. INSERTION SEQUENCES
 Insertion Sequences elements are the simplest transposable elements found in
prokaryotes, encoding only genes for mobilization and insertion of its DNA
 IS elements are commonly found in bacterial chromosomes and plasmids.
 IS elements were first identified in E. coli’s galactose operon, where some mutations were
shown to result from insertion of a DNA sequence now called IS1.
 Prokaryotic IS elements range in size from 768 bp to over 5 kb. Known E. coli IS elements
include.
 IS1 is 768 bp long, and present in 4–19 copies on the E. coli chromosome.
 IS2 has 0–12 copies on the chromosome, and 1 copy on the F plasmid.
 IS10 is found in R plasmids.

19.  The end of all sequenced IS elements show inverted terminal repeats (IRs) of 9–41 bp (e.g., IS1 has
23 bp of nearly identical sequence)
 Integration of IS elements may:
 a. Disrupt coding sequences or regulatory regions.
 b. Alter expression of nearby genes by the action of IS element promoters.
 c. Cause deletions and inversions in adjacent DNA.
 d. Serve as a site for crossing-over between duplicated IS elements.

21.  When an IS element transposes :
 a. The original copy stays in place, and a new copy inserts randomly into the
chromosome.
 b. The IS element uses the host cell replication enzymes for precise replication
 c. Transposition requires transposase, an enzyme encoded by the IS element.
 d .Transposase recognizes the IR sequences to initiate transposition.
 e. IS elements insert into the chromosome without sequence homology (illegitimate
recombination) at target sites.
 i. A staggered cut is made in the target site, and the IS element inserted.
 ii. DNA polymerase and ligase fill the gaps, producing small direct repeats of the target site
flanking the IS element (target site duplications).
 f. Mutational analysis shows that IR sequences are the key.

22. Prokaryotic Transposon Element
 These are also called composite transposons and are shown by the symbol Tn. It is made up
of two IS elements, one present at each end of a DNA sequence which contains genes
whose functions are not related to the transposition process.
 These transposons have been found to have inverted repeats at the ends. The length of
these inverted repeats ranges from a few nucleotides to about 1500 bp.
 It can be said that these are the large transposons which are formed by capturing of an
immobile DNA sequence within two insertion sequences thus enabling it to move.
 Examples of such transposons include the members of Tn series like Tn1, Tn5, Tn9, Tn10,
etc.

23. Transposons in Eukaryotes
a) Transposons in Maize
 Ac-Ds system
b) Transposons in Drosophila
 P-elements
c) Transposons in Human
 SHINs
 LINEs

24. Ac-Ds system
 Ds is derived from Ac by internal deletions
 Ds is not autonomous, requires Ac to move
 Element termini are an imperfect IR
 Ac encodes a protein that promote movement – Transposase.
 Transposase excises element at IR, and also cuts the target.

26.  The Ac- Ds system involves an autonomous element (Ac) whose insertions are unstable,
and a no autonomous element (Ds) whose insertions are stable if only Ds is present.
 McClintock (1950s) showed that some Ds elements derive from Ac elements
 Ac is 4,563 bp, with 11-bp imperfect terminal IRs and 1 transcription unit producing a 3.5
kb mRNA encoding an 807 amino acid transposase. Insertion generates an 8-bp target site
duplication .
 Ac activates Ds to transpose or break the chromosome where it is inserted.
 Ds elements vary in length and sequence, but all have the same terminal IRs as Ac, and
many are deleted or rearranged versions of Ac.
 Unique to corn transposons, timing and frequency of transposition and gene
rearrangements are developmentally regulated

27. P elements
 P elements cause hybrid dysgenesis, a series of defects (mutations, chromosomal
aberrations and sterility) that result from crossing certain Drosophila strains
 i. A mutant lab strain female (M) crossed with a wild- type male (P) will result in hybrid
dysgenesis.
 ii. A mutant lab strain male (M) crossed with a wild- type (P) female (reciprocal cross) will
have normal offspring.
 iii. Thus, hybrid dysgenesis results when chromosomes of the P male parent enter
cytoplasm of an M type oocyte, but cytoplasm from P oocytes does not induce hybrid
dysgenesis.

29. TRANSPOSONS IN HUMANS
 Transposons in humans are in the form of repetitive DNA which consists of sequences that
are interspersed within the entire human genome. These sequences are transposable and
can move to different locations within the genome.
(1) SINEs (Short Interspersed Elements)
 They are ~ 300 bp long and may be present about 5 lakh times in human genome. Alu
sequences are the best characterized SINEs in humans.
 These are termed as ‘Alu’ elements because they contain specific nucleotide sequences
which are cleaved by the restriction enzyme named AluI.
 Alu elements contain Direct Terminal Repeats (DTR) of 7-20 bp length. These DTRs help
them in the insertion process during transposition.

30. (2) LINEs
 Lines ( Long Interspersed Elements):
 They are ~ 6400 bp long and are present about 1 lakh times in the human genome.
 Most prominent example is L1 sequence.
 These transposable elements are some of the most abundant and common families of
moderately repeated sequences in human DNA.

31. Application
 Transposon 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.
 Genetic mutation creates genetic diversity which keeps the population healthy.

32. Effects
 Gene inactivation
 Mutation
 Gene alterations (Insertions, excisions, Duplication or translocation)
 Moderate gene expression or induce recombination
Diseases caused by transposons include
 hemophilia A and B
 severe combined immunodeficiency
 Porphyria
 Cancer
 Duchenne muscular dystrophy