Transposons in bacteria

PRATHYUSHA
Msc.BIOTECHNOLOGY
SCHOOL OF BIOSCIENCES
MAHATMA GANDHI UNIVERSITY
‘’Jumping Genes’’
 Special segments of DNA that can move around to
different positions in the genome of a single cell.
 Found in almost all organisms.
 Mainly known as “transposable elements”.
 Can move from one site to another in the same or
different DNA by the process called transposition.
 Any gene into which a transposable element inserts
itself can no longer function.
 First recognised as mutagens.
HISTORY!!!!!
These elements were first
identified more than 50 years
ago by geneticist Barbara
McClintock of Cold Spring
Harbour Laboratory in New
York. McClintock, however, was
among the first researchers to
suggest that these mysterious
mobile elements of the genome
might play some kind of
regulatory role, determining
which genes are turned on and
when this activation takes place.
In 1983 the Nobel Prize in
Physiology or Medicine was
awarded.
MAIZE
Barbara McClintock
studied about
transposons in maize.
They are also found in
almost all
organisms(prokaryotes &
eukaryotes) and typical
in large numbers. For
example , TE’s make up~
50% of human genome &
70% of maize genome.
Class 1 transposons or Retrotransposons
Class 2 transposons or DNA transposons
CLASS 2- DNA TRANSPOSONS
 “Cut and Paste” mechanism.
 Cut out of its location & inserted to new location.
 Requires enzyme transposase.
 Transposase are encoded within some of these
transposons.
 Transposase binds to:
 Both ends of transposons which consist of inverted
repeats (identical sequences reading in opposite
directions).
 A sequence of DNA that makes up the target site. Some
transposons require target site : others can insert
anywhere.
 The DNA is cut in an offset manner(like “sticky ends” produced by
some restriction enzymes).
 The transposon is ligated into host DNA.
 The gaps are filled by “Watson & Crick” base pairing.
 This creates identical direct repeats at each ends of the transposon.
 Often transposon lose their gene for enzyme. But somewhere in the
cell there is a transposon that can synthesise the enzyme , their
inverted repeats are recognized and they , too , can be moved to a
new location.
Transposons in bacteria
MAIZE Drosophila
TRANSPOSONS IN MAIZE & Drosophila
 1st transposon discovered by
Barbara McClintock.
 Worked with maize(Zea mays).
 Responsible for variety of gene
mutations, especially :
 Insertions & deletions
 Translocations.
 In developing somatic tissues
like corn kernels ,a mutation(ex
; c) that alters colours will be
passed onto all the descendant
cells.
 Awarded Nobel Prize in 1983.
 P elements.
 Do little harm : gene expression is
usually repressed.
 When male flies containing P
elements mate with female flies
lacking them, the transposase
become active in germ line
producing so many mutations
that their off springs are sterile.
 Transgenic flies with any desired
gene can be produced by
injecting the early embryo with
an engineered P element
containing that gene.
Transposons in bacteria
TRANSPOSONS IN BACTERIA
 Requires additional enzyme “resolvase”.
 Carry genes for one or more imparting resistance
to antibiotics.
 When such a transposon is incorporated in
a plasmid, it can leave the host cell and move to
another. This is the way that the alarming
phenomenon of multidrug antibiotic
resistance spreads so rapidly.
INSERTION SEQUENCE
 Segments of bacterial DNA.
 When IS elements appear in the middle of genes, they
interrupt the coding sequence and inactivate the expression
of that gene.
 Owing to their size and in some cases the presence of
transcription and translation termination signals, IS
elements can also block the expression of other genes in the
same operon.
 IS elements were first found in E. coli in the gal operon—a
set of three genes taking part in the metabolism of the sugar
galactose.
These are relatively short, not exceeding
2000 bp (2kb).
1st IS in E.coli : IS 1 (800 bp long).
Types :
 IS 2
 IS 3
 IS 4
 IS 5
TRANSPOSON (tn) ELEMENTS
 Like IS units, Tn elements are mobile in both bacterial
and viral chromosomes and in plasmids.
 Provide a mechanism for the movement of genetic
information from place to place both within and
between organisms.
 Susumu Mitusuhashi first suggested that the genes
responsible for resistance to several antibiotics were
mobile and could move between bacterial plasmids and
chromosomes.
BACTERIOPHAGES
 Behave in a similar fashion.
 Ability to insert their
genetic material into the
host organism.
 Bacteriophage Mu can
insert its DNA at various
places in the E.coli
organisms.
 Like IS units, if insertion
occurs within a gene,
mutant behaviour results at
that locus.
 Here it move by “copy &
paste” mechanism.
CLASS 1- RETROTRANSPOSONS
 “Copy & Paste” mechanism.
 Copy is made of RNA not DNA.
 RNA DNA.
 Long terminal repeats present(in many having 1000
bp’s).
 Generate direct repeats at their new sites of
insertion.
 Presence of these direct repeats indicate
occurrence of retro transposition.
 Some 50% of entire human genome contain RT.
REVERSE TRANSCRIPTASE
LINE......
 Human genome contains over 1 million lines.
 Most abundant of these belong to family : Line1.
 L1 elements are DNA sequences ranging from few 100 to
9000 bp’s.
 Only 50 L1 elements are functional ; that is they can be
transcribed and translated.
 Functional elements are 6500 bp long.
 Encode 3 proteins , including
 Endonuclease that cut DNA & a
 Reverse transcriptase that makes DNA copy of RNA
transcript.
L1 ACTIVITY
L1 DNA
L1 DNA
RNA PROTEINS
L1 element
R
N
A
P
O
L
2
TRANSLATION
Endonuclease cuts a strand
of “target DNA” , often in
the intron of a gene.
RNA &
PROTEINS RE-
ENTER THE
NUCLEUS
RT
 Occasionally , Li activity makes and inserts a copy of
cellular mRNA (thus a natural cDNA). Lacking introns
as well as necessary control elements like promoters ,
these genes are not expressed. They represent one
category of pseudo gene.
 Through this copy mechanism , the no: of Lines can
increase in the genome.
 The diversity of Lines between individual human
genomes makes them useful markers for DNA
“fingerprinting” .
HIV-1
 Cause of AIDS & other human retroviruses(e.g.,HTLV-
1,the human T-cell leukaemia or lymphoma virus)
 The RNA genome contains a gene for
 Reverse transcriptase and one for
 Integrase. Integrase ~ transposase. DNA copies can
be inserted anywhere in the genome.
 Molecules of both the enzymes are incorporated in the
virus particle.
Transposons in bacteria
TRANSPOSONS & MUTATIONS
 Transposons are mutagens.
 Can cause mutation in several ways..
1. Insertions into introns , exons , & even into the DNA
flanking the genes can destroy or alter genes activity.
2. Faulty repair at the old site(cut & paste transposition).
3. Commonest cause of duplications.
 Some cases of human genetic diseases include:
 Haemophilia A(f8) & Haemophilia B(f9).
 X-linked SCID.
 Porphyria.
 Predisposition to colon polyps & cancer.
 Duchenne muscular dystrophy.
PRACTICAL APPLICATIONS
As a result of the capacity of transposon mutagenesis to incorporate
genes into most areas of target chromosomes, there are a number of
functions associated with the process.
 Virulence genes in viruses and bacteria can be discovered by
disrupting genes and observing for a change in phenotype. This
has importance in antibiotic production and disease control.
 Non-essential genes can be discovered by inducing transposon
mutagenesis in an organism. The transformed genes can then be
identified by performing PCR on the organism's recovered
genome.
 Cancer-causing genes can be identified by genome-wide
mutagenesis and screening of mutants containing tumours.
Based on the mechanism and results of the mutation, cancer-
causing genes can be identified as oncogenes or tumour-
suppressor genes.
What good are transposons?
 Transposons have been called "junk" DNA and "selfish"
DNA.
 "selfish" because their only function seems to make
more copies of themselves
&
 "junk" because there is no obvious benefit to their host.
 Retrotransposons often carry some additional sequences
at their 3' end as they insert into a new location.
 Create new combinations of exons, promoters, and
enhancers that benefit the host.
 The longer the L1 element, the lower the level of gene
expression.
 L1 elements inserted into the introns of functional
genes reduce the transcription of those genes without
harming the gene product.
 Some 79% of our genes contain L1 elements, and
perhaps they are a mechanism for establishing the
baseline level of gene activity.
 Telomerase, the enzyme essential for maintaining
chromosome length, is closely related to the reverse
transcriptase of LINEs and may have evolved from it.
 RAG-1 and RAG-2.
 The proteins encoded by these genes are needed to
assemble the repertoire of antibodies and T-cells
receptors (TCRs) used by the adaptive immune system .
 The mechanism resembles that of the cut and paste
method of Class II transposons , and the RAG genes
may have evolved from them. If so, the event occurred
some 450 million years ago when the jawed vertebrates
evolved from jawless ancestors. Only jawed vertebrates
have the RAG-1 and RAG-2 genes.
 In Drosophila, the insertion of transposons into genes has
been linked to the development of resistance
to DDT and organophosphate insecticides.
Transposons in bacteria
Transposons in bacteria
1 sur 28

Recommandé

Transposable elements in Maize And Drosophila par
Transposable elements in Maize And DrosophilaTransposable elements in Maize And Drosophila
Transposable elements in Maize And DrosophilaSubhradeep sarkar
31.9K vues30 diapositives
Transformation in bacteria par
Transformation in bacteriaTransformation in bacteria
Transformation in bacteriaMona Othman Albureikan / King Abdulaziz University
113.2K vues14 diapositives
Transposones par
TransposonesTransposones
Transposonesmicrobiology Notes
64.1K vues36 diapositives
Spontaneous and induced mutations par
Spontaneous and induced mutationsSpontaneous and induced mutations
Spontaneous and induced mutationsSreeraj Thamban
131.2K vues28 diapositives
Bacterial Transposons par
Bacterial TransposonsBacterial Transposons
Bacterial Transposonsguest06ad101
58.8K vues36 diapositives
Gene silencing par
Gene silencing Gene silencing
Gene silencing Parvez Sheik
112.3K vues29 diapositives

Contenu connexe

Tendances

TRANSPOSABLE ELEMENTS par
TRANSPOSABLE ELEMENTSTRANSPOSABLE ELEMENTS
TRANSPOSABLE ELEMENTSAmbica Parthasarathi
118.5K vues33 diapositives
Holliday model of crossing over par
Holliday model of crossing overHolliday model of crossing over
Holliday model of crossing overNethravathi Siri
17.8K vues2 diapositives
Prokaryotic genome organization par
Prokaryotic genome organizationProkaryotic genome organization
Prokaryotic genome organizationmanojsiddartha bolthajira
61.5K vues38 diapositives
Regulation of gene expression in prokaryotes par
Regulation of gene expression in prokaryotesRegulation of gene expression in prokaryotes
Regulation of gene expression in prokaryotesgohil sanjay bhagvanji
27.4K vues30 diapositives
Complementation test; AC-DS System in Maize par
Complementation test; AC-DS System in MaizeComplementation test; AC-DS System in Maize
Complementation test; AC-DS System in MaizeAVKaaviya
3.9K vues9 diapositives
TRANSPOSABLE ELEMENTS par
TRANSPOSABLE   ELEMENTSTRANSPOSABLE   ELEMENTS
TRANSPOSABLE ELEMENTSseetugulia
17K vues19 diapositives

Tendances(20)

Complementation test; AC-DS System in Maize par AVKaaviya
Complementation test; AC-DS System in MaizeComplementation test; AC-DS System in Maize
Complementation test; AC-DS System in Maize
AVKaaviya3.9K vues
TRANSPOSABLE ELEMENTS par seetugulia
TRANSPOSABLE   ELEMENTSTRANSPOSABLE   ELEMENTS
TRANSPOSABLE ELEMENTS
seetugulia17K vues
Molecular mechanism of Mutation par Achyut Bora
Molecular mechanism of MutationMolecular mechanism of Mutation
Molecular mechanism of Mutation
Achyut Bora28.5K vues
Molecular basis of mutations par Shalini Saini
Molecular basis of mutationsMolecular basis of mutations
Molecular basis of mutations
Shalini Saini53.6K vues
Gene regulation in eukaryotes par Iqra Wazir
Gene regulation in eukaryotesGene regulation in eukaryotes
Gene regulation in eukaryotes
Iqra Wazir23.4K vues
Transformation par sridevi244
TransformationTransformation
Transformation
sridevi24431.3K vues

Similaire à Transposons in bacteria

STRUCTURE OF TRANSPOSONS.docx par
STRUCTURE OF TRANSPOSONS.docxSTRUCTURE OF TRANSPOSONS.docx
STRUCTURE OF TRANSPOSONS.docxERRAMNAGENDRAM
67 vues4 diapositives
Transposable elements par
Transposable elementsTransposable elements
Transposable elementsRajwantiSaran
1.5K vues68 diapositives
Transposons par
TransposonsTransposons
TransposonsRinaldo John
282 vues29 diapositives
Bacterial transposable elements par
Bacterial transposable elementsBacterial transposable elements
Bacterial transposable elementsTejaswini Petkar
1.2K vues23 diapositives
Transposable elements par
Transposable elementsTransposable elements
Transposable elementsMehmet Gülçimen
3.4K vues26 diapositives
transposons.ppt par
transposons.ppttransposons.ppt
transposons.pptPudhuvai Baveesh
357 vues25 diapositives

Similaire à Transposons in bacteria(20)

Reeta yadav. roll no. 01. transposable elements in prokaryotes par Manisha Jangra
Reeta yadav. roll no. 01. transposable elements in prokaryotesReeta yadav. roll no. 01. transposable elements in prokaryotes
Reeta yadav. roll no. 01. transposable elements in prokaryotes
Manisha Jangra4.9K vues
Transposable elements - MAYUR SONAGARA par MAYUR SONAGARA
Transposable elements - MAYUR SONAGARATransposable elements - MAYUR SONAGARA
Transposable elements - MAYUR SONAGARA
MAYUR SONAGARA297 vues
type of genes - jumping genes par saharzaidi178
type of genes - jumping genestype of genes - jumping genes
type of genes - jumping genes
saharzaidi1785.9K vues
Regulation of eukaryotic gene expression par Md Murad Khan
Regulation of eukaryotic gene expressionRegulation of eukaryotic gene expression
Regulation of eukaryotic gene expression
Md Murad Khan20.1K vues
TRANSPOSABLE ELEMENTS par seetugulia
TRANSPOSABLE ELEMENTSTRANSPOSABLE ELEMENTS
TRANSPOSABLE ELEMENTS
seetugulia1K vues
Selman A. Wakman award for Carol A. Gross par kokilaM9
Selman A. Wakman award for Carol A. GrossSelman A. Wakman award for Carol A. Gross
Selman A. Wakman award for Carol A. Gross
kokilaM926 vues
What are TEs Comment on Are there any distinctive features Why might.pdf par architcreation
What are TEs Comment on Are there any distinctive features Why might.pdfWhat are TEs Comment on Are there any distinctive features Why might.pdf
What are TEs Comment on Are there any distinctive features Why might.pdf

Plus de Raviz Prathyusha

Electrophoresis par
ElectrophoresisElectrophoresis
ElectrophoresisRaviz Prathyusha
159.6K vues43 diapositives
Scid mice par
Scid miceScid mice
Scid miceRaviz Prathyusha
3.5K vues13 diapositives
Good laboratory practises par
Good laboratory practisesGood laboratory practises
Good laboratory practisesRaviz Prathyusha
6.4K vues73 diapositives
Forces stabilising structure of proteins par
Forces stabilising structure of proteinsForces stabilising structure of proteins
Forces stabilising structure of proteinsRaviz Prathyusha
17.9K vues25 diapositives
Functions of kidney par
Functions of kidneyFunctions of kidney
Functions of kidneyRaviz Prathyusha
58.1K vues18 diapositives
Dna damage checkpoints par
Dna damage checkpointsDna damage checkpoints
Dna damage checkpointsRaviz Prathyusha
15.7K vues33 diapositives

Dernier

Psychology KS4 par
Psychology KS4Psychology KS4
Psychology KS4WestHatch
68 vues4 diapositives
Dance KS5 Breakdown par
Dance KS5 BreakdownDance KS5 Breakdown
Dance KS5 BreakdownWestHatch
68 vues2 diapositives
AUDIENCE - BANDURA.pptx par
AUDIENCE - BANDURA.pptxAUDIENCE - BANDURA.pptx
AUDIENCE - BANDURA.pptxiammrhaywood
69 vues44 diapositives
Structure and Functions of Cell.pdf par
Structure and Functions of Cell.pdfStructure and Functions of Cell.pdf
Structure and Functions of Cell.pdfNithya Murugan
368 vues10 diapositives
Psychology KS5 par
Psychology KS5Psychology KS5
Psychology KS5WestHatch
77 vues5 diapositives
ISO/IEC 27001 and ISO/IEC 27005: Managing AI Risks Effectively par
ISO/IEC 27001 and ISO/IEC 27005: Managing AI Risks EffectivelyISO/IEC 27001 and ISO/IEC 27005: Managing AI Risks Effectively
ISO/IEC 27001 and ISO/IEC 27005: Managing AI Risks EffectivelyPECB
545 vues18 diapositives

Dernier(20)

Dance KS5 Breakdown par WestHatch
Dance KS5 BreakdownDance KS5 Breakdown
Dance KS5 Breakdown
WestHatch68 vues
Structure and Functions of Cell.pdf par Nithya Murugan
Structure and Functions of Cell.pdfStructure and Functions of Cell.pdf
Structure and Functions of Cell.pdf
Nithya Murugan368 vues
ISO/IEC 27001 and ISO/IEC 27005: Managing AI Risks Effectively par PECB
ISO/IEC 27001 and ISO/IEC 27005: Managing AI Risks EffectivelyISO/IEC 27001 and ISO/IEC 27005: Managing AI Risks Effectively
ISO/IEC 27001 and ISO/IEC 27005: Managing AI Risks Effectively
PECB 545 vues
Narration ppt.pptx par TARIQ KHAN
Narration  ppt.pptxNarration  ppt.pptx
Narration ppt.pptx
TARIQ KHAN119 vues
The basics - information, data, technology and systems.pdf par JonathanCovena1
The basics - information, data, technology and systems.pdfThe basics - information, data, technology and systems.pdf
The basics - information, data, technology and systems.pdf
JonathanCovena188 vues
Class 10 English notes 23-24.pptx par TARIQ KHAN
Class 10 English notes 23-24.pptxClass 10 English notes 23-24.pptx
Class 10 English notes 23-24.pptx
TARIQ KHAN107 vues
OEB 2023 Co-learning To Speed Up AI Implementation in Courses.pptx par Inge de Waard
OEB 2023 Co-learning To Speed Up AI Implementation in Courses.pptxOEB 2023 Co-learning To Speed Up AI Implementation in Courses.pptx
OEB 2023 Co-learning To Speed Up AI Implementation in Courses.pptx
Inge de Waard167 vues
JiscOAWeek_LAIR_slides_October2023.pptx par Jisc
JiscOAWeek_LAIR_slides_October2023.pptxJiscOAWeek_LAIR_slides_October2023.pptx
JiscOAWeek_LAIR_slides_October2023.pptx
Jisc79 vues
11.30.23 Poverty and Inequality in America.pptx par mary850239
11.30.23 Poverty and Inequality in America.pptx11.30.23 Poverty and Inequality in America.pptx
11.30.23 Poverty and Inequality in America.pptx
mary850239144 vues
Lecture: Open Innovation par Michal Hron
Lecture: Open InnovationLecture: Open Innovation
Lecture: Open Innovation
Michal Hron96 vues
Narration lesson plan.docx par TARIQ KHAN
Narration lesson plan.docxNarration lesson plan.docx
Narration lesson plan.docx
TARIQ KHAN104 vues
EIT-Digital_Spohrer_AI_Intro 20231128 v1.pptx par ISSIP
EIT-Digital_Spohrer_AI_Intro 20231128 v1.pptxEIT-Digital_Spohrer_AI_Intro 20231128 v1.pptx
EIT-Digital_Spohrer_AI_Intro 20231128 v1.pptx
ISSIP317 vues
UWP OA Week Presentation (1).pptx par Jisc
UWP OA Week Presentation (1).pptxUWP OA Week Presentation (1).pptx
UWP OA Week Presentation (1).pptx
Jisc74 vues
Scope of Biochemistry.pptx par shoba shoba
Scope of Biochemistry.pptxScope of Biochemistry.pptx
Scope of Biochemistry.pptx
shoba shoba124 vues

Transposons in bacteria

  • 2. ‘’Jumping Genes’’  Special segments of DNA that can move around to different positions in the genome of a single cell.  Found in almost all organisms.  Mainly known as “transposable elements”.  Can move from one site to another in the same or different DNA by the process called transposition.  Any gene into which a transposable element inserts itself can no longer function.  First recognised as mutagens.
  • 3. HISTORY!!!!! These elements were first identified more than 50 years ago by geneticist Barbara McClintock of Cold Spring Harbour Laboratory in New York. McClintock, however, was among the first researchers to suggest that these mysterious mobile elements of the genome might play some kind of regulatory role, determining which genes are turned on and when this activation takes place. In 1983 the Nobel Prize in Physiology or Medicine was awarded.
  • 4. MAIZE Barbara McClintock studied about transposons in maize. They are also found in almost all organisms(prokaryotes & eukaryotes) and typical in large numbers. For example , TE’s make up~ 50% of human genome & 70% of maize genome.
  • 5. Class 1 transposons or Retrotransposons Class 2 transposons or DNA transposons
  • 6. CLASS 2- DNA TRANSPOSONS  “Cut and Paste” mechanism.  Cut out of its location & inserted to new location.  Requires enzyme transposase.  Transposase are encoded within some of these transposons.  Transposase binds to:  Both ends of transposons which consist of inverted repeats (identical sequences reading in opposite directions).  A sequence of DNA that makes up the target site. Some transposons require target site : others can insert anywhere.
  • 7.  The DNA is cut in an offset manner(like “sticky ends” produced by some restriction enzymes).  The transposon is ligated into host DNA.  The gaps are filled by “Watson & Crick” base pairing.  This creates identical direct repeats at each ends of the transposon.  Often transposon lose their gene for enzyme. But somewhere in the cell there is a transposon that can synthesise the enzyme , their inverted repeats are recognized and they , too , can be moved to a new location.
  • 9. MAIZE Drosophila TRANSPOSONS IN MAIZE & Drosophila  1st transposon discovered by Barbara McClintock.  Worked with maize(Zea mays).  Responsible for variety of gene mutations, especially :  Insertions & deletions  Translocations.  In developing somatic tissues like corn kernels ,a mutation(ex ; c) that alters colours will be passed onto all the descendant cells.  Awarded Nobel Prize in 1983.  P elements.  Do little harm : gene expression is usually repressed.  When male flies containing P elements mate with female flies lacking them, the transposase become active in germ line producing so many mutations that their off springs are sterile.  Transgenic flies with any desired gene can be produced by injecting the early embryo with an engineered P element containing that gene.
  • 11. TRANSPOSONS IN BACTERIA  Requires additional enzyme “resolvase”.  Carry genes for one or more imparting resistance to antibiotics.  When such a transposon is incorporated in a plasmid, it can leave the host cell and move to another. This is the way that the alarming phenomenon of multidrug antibiotic resistance spreads so rapidly.
  • 12. INSERTION SEQUENCE  Segments of bacterial DNA.  When IS elements appear in the middle of genes, they interrupt the coding sequence and inactivate the expression of that gene.  Owing to their size and in some cases the presence of transcription and translation termination signals, IS elements can also block the expression of other genes in the same operon.  IS elements were first found in E. coli in the gal operon—a set of three genes taking part in the metabolism of the sugar galactose.
  • 13. These are relatively short, not exceeding 2000 bp (2kb). 1st IS in E.coli : IS 1 (800 bp long). Types :  IS 2  IS 3  IS 4  IS 5
  • 14. TRANSPOSON (tn) ELEMENTS  Like IS units, Tn elements are mobile in both bacterial and viral chromosomes and in plasmids.  Provide a mechanism for the movement of genetic information from place to place both within and between organisms.  Susumu Mitusuhashi first suggested that the genes responsible for resistance to several antibiotics were mobile and could move between bacterial plasmids and chromosomes.
  • 15. BACTERIOPHAGES  Behave in a similar fashion.  Ability to insert their genetic material into the host organism.  Bacteriophage Mu can insert its DNA at various places in the E.coli organisms.  Like IS units, if insertion occurs within a gene, mutant behaviour results at that locus.  Here it move by “copy & paste” mechanism.
  • 16. CLASS 1- RETROTRANSPOSONS  “Copy & Paste” mechanism.  Copy is made of RNA not DNA.  RNA DNA.  Long terminal repeats present(in many having 1000 bp’s).  Generate direct repeats at their new sites of insertion.  Presence of these direct repeats indicate occurrence of retro transposition.  Some 50% of entire human genome contain RT. REVERSE TRANSCRIPTASE
  • 17. LINE......  Human genome contains over 1 million lines.  Most abundant of these belong to family : Line1.  L1 elements are DNA sequences ranging from few 100 to 9000 bp’s.  Only 50 L1 elements are functional ; that is they can be transcribed and translated.  Functional elements are 6500 bp long.  Encode 3 proteins , including  Endonuclease that cut DNA & a  Reverse transcriptase that makes DNA copy of RNA transcript.
  • 18. L1 ACTIVITY L1 DNA L1 DNA RNA PROTEINS L1 element R N A P O L 2 TRANSLATION Endonuclease cuts a strand of “target DNA” , often in the intron of a gene. RNA & PROTEINS RE- ENTER THE NUCLEUS RT
  • 19.  Occasionally , Li activity makes and inserts a copy of cellular mRNA (thus a natural cDNA). Lacking introns as well as necessary control elements like promoters , these genes are not expressed. They represent one category of pseudo gene.  Through this copy mechanism , the no: of Lines can increase in the genome.  The diversity of Lines between individual human genomes makes them useful markers for DNA “fingerprinting” .
  • 20. HIV-1  Cause of AIDS & other human retroviruses(e.g.,HTLV- 1,the human T-cell leukaemia or lymphoma virus)  The RNA genome contains a gene for  Reverse transcriptase and one for  Integrase. Integrase ~ transposase. DNA copies can be inserted anywhere in the genome.  Molecules of both the enzymes are incorporated in the virus particle.
  • 22. TRANSPOSONS & MUTATIONS  Transposons are mutagens.  Can cause mutation in several ways.. 1. Insertions into introns , exons , & even into the DNA flanking the genes can destroy or alter genes activity. 2. Faulty repair at the old site(cut & paste transposition). 3. Commonest cause of duplications.  Some cases of human genetic diseases include:  Haemophilia A(f8) & Haemophilia B(f9).  X-linked SCID.  Porphyria.  Predisposition to colon polyps & cancer.  Duchenne muscular dystrophy.
  • 23. PRACTICAL APPLICATIONS As a result of the capacity of transposon mutagenesis to incorporate genes into most areas of target chromosomes, there are a number of functions associated with the process.  Virulence genes in viruses and bacteria can be discovered by disrupting genes and observing for a change in phenotype. This has importance in antibiotic production and disease control.  Non-essential genes can be discovered by inducing transposon mutagenesis in an organism. The transformed genes can then be identified by performing PCR on the organism's recovered genome.  Cancer-causing genes can be identified by genome-wide mutagenesis and screening of mutants containing tumours. Based on the mechanism and results of the mutation, cancer- causing genes can be identified as oncogenes or tumour- suppressor genes.
  • 24. What good are transposons?  Transposons have been called "junk" DNA and "selfish" DNA.  "selfish" because their only function seems to make more copies of themselves &  "junk" because there is no obvious benefit to their host.  Retrotransposons often carry some additional sequences at their 3' end as they insert into a new location.  Create new combinations of exons, promoters, and enhancers that benefit the host.
  • 25.  The longer the L1 element, the lower the level of gene expression.  L1 elements inserted into the introns of functional genes reduce the transcription of those genes without harming the gene product.  Some 79% of our genes contain L1 elements, and perhaps they are a mechanism for establishing the baseline level of gene activity.  Telomerase, the enzyme essential for maintaining chromosome length, is closely related to the reverse transcriptase of LINEs and may have evolved from it.
  • 26.  RAG-1 and RAG-2.  The proteins encoded by these genes are needed to assemble the repertoire of antibodies and T-cells receptors (TCRs) used by the adaptive immune system .  The mechanism resembles that of the cut and paste method of Class II transposons , and the RAG genes may have evolved from them. If so, the event occurred some 450 million years ago when the jawed vertebrates evolved from jawless ancestors. Only jawed vertebrates have the RAG-1 and RAG-2 genes.  In Drosophila, the insertion of transposons into genes has been linked to the development of resistance to DDT and organophosphate insecticides.