The Nature of Transposons Chapter 11 pp 300-315

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The Nature of Transposons Chapter 11 pp 300-315

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The Nature of Transposons Chapter 11 pp 300-315. Outline. Nature of Transposons Transposons Prokaryotic Eukaryotic: Dr. McClintock’s research Retrotransposons vs Retroviruses. Transposons. Are mobile DNA sometimes referred to as “jumping genes”. Why are transposons in our genome?. - PowerPoint PPT Presentation

Transcript of The Nature of Transposons Chapter 11 pp 300-315

Page 1: The Nature of Transposons Chapter 11 pp 300-315

The Nature of TransposonsChapter 11pp 300-315

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Outline• Nature of Transposons

• Transposons – Prokaryotic– Eukaryotic: Dr. McClintock’s research

• Retrotransposons vs Retroviruses

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Transposons

• Are mobile DNA sometimes referred to as “jumping genes”.

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Why are transposons in our genome?

• Cellular function hypothesis– Antibody diversity of VDJ

• Genetic variation hypothesis

• Self-DNA hypothesis

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Common features associated with transposons

1. Direct repeats

2. Terminal Inverted repeats

CommonFeatures

Are:

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Mechanisms of Transposition

• Movement through DNA intermediates

• Movement through RNA intermediates

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• Movement through DNA intermediates

DNA TranspositionC

ut and Paste

Replicative Non-Replicative

Copy and Paste

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Non-Replicative Movement by Transposition

• Requires transposase

• 1) Transposase cuts transposon out of donor DNA (blunt cut)

• 2) Transposase makes a staggered cut at the target sequence

• 3) Transposase ligates transposon into the target

• 4) Gaps are filled in with DNA pol I and ligase

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Staggered cut

Direct repeats are generated

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Staggered cut

Direct repeats are generated

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Examples of: Transposable Elements in Bacteria

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1. Simple Bacterial Transposon

INSERTION SEQUENCE

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2. COMPOSITE TRANSPOSONIS + any DNA segment

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Dr. Barbara McClintock1902-1992

Nobel Prize, 1983Physiology or Medicine

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“I don’t understand a word that she said, but if she says it is so, it must

be so!”

Alfred Sturtevant

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The Ds element often results in chromosomal breakage

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Drosophilia melanogaster&

DNA transposition

“The P Element”

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The P element Codes for both

• Transposase

• Repressor of transposition

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Offspring sterile

Offspring norm

al

Why the difference?

Female P- and male P+ Female P+ and male P-

Hybrid dysgenesis Non-hybrid dysgenesis

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Remember the P element Codes for

• A Transposase

• AND

• A Repressor of transposition

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Retrotransposons

mRNADNA

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Examples of retrotransposons elements

• Ty

• Copia

• Alu

Yeast

Drosophila

Humans

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General MechanismOf Retrotransposons

Note: retrotransposons are not found in prokaryotes

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Types of Retrotransposons

• Ty

• Copia

Yeast

Drosophila

Humans

Viral

Non-Viral• Alu

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Non-viral Retrotransposons

Humans

Non-Viral

LINES SINES

Alu Example: Line 1 and Line 2

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ALU

• 300 bp

• Endonuclease cutting site: site5' AG/CT 3‘

• Retrotransposon

• 1 million in genome

• Linked to variety of disorders

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Alu has inserted in NF-1 gene

Neurofibromatosis: autosomal dominantGrowth of nodules mainly affecting nerves in the skin

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Viral retrotransposons look a little like retroviruses—but are NOT the same !

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Now we must compare a Viral RNA with a Viral Retrotransposon

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VIRAL RNA

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Now a viral retrotransposon

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Here’s the Copia element of Drosophila

Compare to the retrovirus

Similar gag and pol sequences

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Here’s the Ty element, again notice similarities to retroviruses

Delta sequences function like LTR’s in viruses

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Summary Table

Viral and non-viralTy and Copia viral retrotransposons

Alu non viral retrotransposons

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A topic of scientific discussion is what is a “prion”?

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Blunt cut from donor

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HUMANIMMUNODEFICIENCYVIRUS

Human Helper T Lymphocyte