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Mobile DNA Sequences in the Genome. Gene Technology. Lecture 8 – Chapter 7. Barbara McClintock (nobel prize winner 1983) Found in the late 1940s -> genetic elements in maize can direct their own movement within the genome. Mobile DNA Sequences in the Genome. Gene Technology.
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Mobile DNA Sequences in the Genome Gene Technology Lecture 8 – Chapter 7 Barbara McClintock (nobel prize winner 1983) Found in the late 1940s -> genetic elements in maize can direct their own movement within the genome
Mobile DNA Sequences in the Genome Gene Technology Mobile Elements: -> can be found in all organisms -> 50% of human genome -> interfere with gene expression -> generating mutations (-> Evolution) -> reorganize genomic structure Lecture 7 – Chapter 7
Mutation can be caused by insertions: Mutation in the gal operon was moved to λ phage Gene Technology Insertion
Mobile elements -> Intergration into genome Gene Technology
Principle of mobile elements -> Intergration into genome Gene Technology Transposase-> Enzyme coded on mobile elements -> resposible for excition and integration
Insertion Element (IS): -> most simple mobile elements -> found mainly in bacteria Gene Technology IS element is cut out and leaves behind flanking repeats (non replicative) -> orginal target sequence are increased after jumb
Insertion Element (IS): Gene Technology
Transposons (TN): -> More complex mobile elements -> found in all organisms Transposons: Transposons carry frequently antibiotic resistence genes Transposons can jump from genome to phage or conjugative plasmid -> gene transfere to other bacteria (problem with antibiotica resistent bacteria) Gene Technology
Transposons Gene Technology Composite Transposon: -> Insertion elements on both end of the transposon (one active transposase – one inactive transposase) Simple Transposons: -> Inverted repeats on both ends -> Transposase and Resolvase -> responsible for transfer
Transposons Simple Transposon (Tn3): -> Replicative transposition -> after the jump both have a copy of the transposon Composite Transposons (Tn10): ->non replicative (conservative) -> like tranposition of IS elements Gene Technology
Transposons Gene Technology
Transposons Simple Transposon (Tn3): -> Replicative transposition -> after the jump both have a copy of the transposon Transposase: responsible for excition and transfer Resolvase: responsible for resolution -> replicative transfer Gene Technology
Transposons Gene Technology An R plasmid may contain several transposons carrying (resistance genes)
Transposons Composite transposons: -> non replicative transfer Ac element (first discovered in maize) -> Activator (avtive transposon) Ds element (first discovered in maize) -> Dissociation -> passive transposon-> needs Ac to move Gene Technology
Transposons Composite transposons: -> non replicative transfer Ac element (first discovered in maize) -> Activator (avtive transposon) Ds element (first discovered in maize) -> Dissociation -> passive transposon-> needs Ac to move Gene Technology Deletions in Ac element -> gives Ds element -> inactive transposase -> needs Ac to move
Mechanism of Ac or Ds tranfer Gene Technology
Transposons Transposition has influence on phenotype of maize First recognized by Barbara McKintock (first transposon found) Gene Technology Movement of Transposon during development of fruit -> pattern in pigmentation
Transposons Gene Technology
Transposons Transposons are activated by hemimethylated DNA -> right after replication when second strand is not yet methylated When non replicative transposon (Tn10) jumps it leaves a double strand break behind -> repaired by using other stand (with transposon in) as template (repair pathway) -> in the end both strand have the transposon in 2 times Not only both cells after replication have the transposon -> also number of transposons increased!!!! Gene Technology
Retrotransposons are similar to retroviruses RNA intermediate + use of reverse transcriptase Gene Technology
Retrotransposons are similar to retroviruses RNA intermediate + use of reverse transcriptase Gene Technology
Transposons versus Retrotransposon Gene Technology
Retrotransposon • There are 2 groups: • LTR (long terminal repeats) retrotransposons (viral like) • Non-LTR retrotransposons (polyA) Gene Technology Carry strong promoters If transposon inserted 5’ to silenced gene -> activates gene expression of these genes Retrotransposons can cause cancer!! Promoter necessary for transposition
Retrotransposon Protein coded for : Integrase + Reverse transcriptase Gene Technology Carry strong promoters for RNA ploymerase If transposon inserted 5’ to silenced gene -> activates gene expression of these genes Retrotransposons can cause cancer!! Retroviruses can also cause cancer!! ORF1: RNA binding protein ORF2: Endonuclease + reverse transcriptase
Retrotransposon Demonstration that retrotransposon transfers through RNA intermediate Ty is yeast LTR retrotransposon Gene Technology
Non-LTR Retrotransposon ORF1: RNA binding protein ORF2: Endonuclease + reverse transcriptase Gene Technology Promoter necessary for transposition mRNA transcript with poly A
Non-LTR Retrotransposon Transposition -> target-primed reverse transcription Reverse transcription commonly stops before element has been fully transcribed -> a lot of truncated L1 elements Alu elements: 300bp repetitive sequences (11% of human genome) -> belong to SINEs (do not encode their own reverse transcriptase -> nonautonomous transposons SINEs are probably trancated LINEs (share same 3’ sequence) Alu elements are activated by LINEs Gene Technology
Types of transposable elements in the human genome Gene Technology
Human genes contain many transposable elements Gene Technology Important for survival -> Exon/Intron concept of a gene
Transposons are mainly responsible for differences in genome size Gene Technology
Transposons can cause Mutations Transposable elements at work in snapdragon Result of transposition or excision -> not always clean excited -> has an effect on enhancer -> different expression level Gene Technology
Transposons can cause Mutations Transposons and retrotransposons can induce mutations by inserting near or within genes. -> transposon-induced mutations are relatively stable, because the sequence at the insertion site is retained as they transpose via the replication mechanism. Gene Technology Most mutations caused by transposons are deleterious -> L1 insertion into hemophilia A Retrotransposons can be responsible for genetic disease (34 diseases identified) -> hemophilia, muscular dystrophy, … Development of genetic disease can happen by transposon jumb in the embryo!!!
Transposons generate diversity for evolution Gene Technology
Transposons generate diversity for evolution Can affect genes (delection, insertion, exchange), regulatory elements Gene Technology
Transposons generate diversity for evolution Can affect genes (delection, insertion, exchange), regulatory elements Gene Technology Mutant receptors -> cannot remove cholesterol from blood
Transposons can be silenced Organisms with high transposition (Drosphila) can silence transposition -> P element encodes not only transposase but also an inhibitor to transpostion (Protein alters slicing of transposase -> inactive transposase) Gene Technology
Transposons can be silenced Gene Technology If female has P element -> oocytes (eggs) with inhibitor produced -> normal flies If female has no P element -> oocytes have burst of transposition in embryo -> steril offspring