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The Nature of Transposons Chapter 11 pp 297-309. Outline. Nature of Transposons Transposons Prokaryotic Eukaryotic: Dr. McClintock’s research Retrotransposons vs Retroviruses. Transposons. Are mobile DNA sometimes referred to as “jumping genes”. - PowerPoint PPT Presentation
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The Nature of TransposonsChapter 11 pp 297-309
Outline• Nature of Transposons
• Transposons – Prokaryotic– Eukaryotic: Dr. McClintock’s research
• Retrotransposons vs Retroviruses
Transposons
• Are mobile DNA sometimes referred to as “jumping genes”.
Common features associated with transposons
1. Direct repeats
2. Terminal Inverted repeats
CommonFeatures
Are:
Transposable Elements in Bacteria
1. Simple Bacterial Transposon
INSERTION SEQUENCE
2. COMPOSITE TRANSPOSONIS + any DNA segment
Dr. Barbara McClintock1902-1992
Nobel Prize, 1983Physiology or Medicine
“I don’t understand a word that she said, but if she says it is so, it must
be so!”
Alfred Sturtevant
“Ds Transposed out”
The Ds element often results in chromosomal breakage
Drosophilia melanogaster&
DNA transposition
“The P Element”
The P element Codes for
• Transposase
• Repressor of transposition
Offspring sterile
Offspring norm
al
Why the difference?
Female P- and male P+ Female P+ and male P-
Hybrid dysgenesis Non-hybrid dysgenesis
Remember the P element Codes for
• A Transposase
• AND
• A Repressor of transposition
Mite
Science. 1991 Sep 6;253(5024):1125-8Possible horizontal transfer of Drosophila genes by the
mite Proctolaelaps regalis.
Houck MA, Clark JB, Peterson KR, Kidwell MG.
D. melanogaster
D. willistoni
The P element took a ride on a
That moved it onto
~50 yrs ago
Retrotransposons
mRNADNA
Examples of retrotransposons elements
• Ty
• Copia
• Alu
Yeast
Drosophila
Humans
General MechanismOf Retrotransposons
Note: retrotransposons are not found in prokaryotes
Types of Retrotransposons
• Ty
• Copia
Yeast
Drosophila
Humans
Viral
Non-Viral• Alu
Non-viral Retrotransposons
Humans
Non-Viral
LINES SINES
Alu Example: Line 1 and Line 2
ALU
• 300 bp
• Endonuclease cutting site: site5' AG/CT 3‘
• Retrotransposon
• 1 million in genome
• Linked to variety of disorders
Alu has inserted in NF-1 gene
Neurofibromatosis: autosomal dominantGrowth of nodules mainly affecting nerves in the skin
Viral retrotransposons look a little like retroviruses—but are NOT the same !
Now we must compare a Viral RNA with a Viral Retrotransposon
VIRAL RNA
Infectious process
Now a viral retrotransposon
Here’s the Copia element of Drosophila
Compare to the retrovirus
Similar gag and pol sequences
Here’s the Ty element, again notice similarities to retroviruses
Delta sequences function like LTR’s in viruses
Summary Table
Viral and non-viralTy and Copia viral retrotransposons
Alu non viral retrotransposons
A topic of scientific discussion is what is a “prion”?
Blunt cut from donor
HUMANIMMUNODEFICIENCYVIRUS
Human Helper T Lymphocyte