1. The Nature of Transposons Chapter 11 pp 300-315

2. Outline Nature of Transposons Transposons
Prokaryotic
Eukaryotic: Dr. McClintock’s research
Retrotransposons vs Retroviruses

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

4. Why are transposons in our genome?
Cellular function hypothesis
Antibody diversity of VDJ
Genetic variation hypothesis
Self-DNA hypothesis

5. Common features associated with transposons
1. Direct repeats
Common
Features
Are:
2. Terminal
Inverted
repeats

7. Mechanisms of Transposition
Movement through DNA intermediates
Movement through RNA intermediates

8. DNA Transposition Movement through DNA intermediates Replicative
Cut and Paste
Copy and Paste
Movement through DNA intermediates
Replicative
Non-Replicative

9. 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

10. Direct repeats are generated
Staggered cut
Direct repeats are generated

11. Direct repeats are generated
Staggered cut
Direct repeats are generated

12. Examples of: Transposable Elements in Bacteria

13. 1. Simple Bacterial Transposon
INSERTION SEQUENCE

14. 2. COMPOSITE TRANSPOSON
IS + any DNA segment

15. Physiology or Medicine
Dr. Barbara McClintock
Nobel Prize, 1983
Physiology or Medicine

16. “I don’t understand a word that she said, but if she says it is so, it must be so!” Alfred Sturtevant

20. The Ds element often results in chromosomal breakage

21. Drosophilia melanogaster & DNA transposition “The P Element”

22. The P element Codes for both
Transposase
Repressor of transposition

23. Female P- and male P+
Female P+ and male P-
Offspring sterile
Offspring normal
Non-hybrid dysgenesis
Hybrid dysgenesis
Why the difference?

24. Remember the P element Codes for
A Transposase
AND
A Repressor of transposition

25. The P element took a ride on a
Science Sep 6;253(5024): Possible horizontal transfer of Drosophila genes by the mite Proctolaelaps regalis. Houck MA, Clark JB, Peterson KR, Kidwell MG.
D. willistoni
The P element took a ride on a
~50 yrs ago
That moved it onto
Mite
D. melanogaster

26. Retrotransposons
mRNA
DNA

27. Examples of retrotransposons elements
Yeast Ty
Copia
Alu
Drosophila
Humans

28. Note: retrotransposons are not found in prokaryotes
General Mechanism
Of Retrotransposons
Note: retrotransposons are not found in prokaryotes

29. Types of Retrotransposons
Humans
Alu
Non-Viral
Yeast Ty
Copia
Viral
Drosophila

30. Non-viral Retrotransposons
Humans
Non-Viral
LINES
SINES
Example:
Line 1 and Line 2
Alu

31. ALU 300 bp Endonuclease cutting site: site5' AG/CT 3‘ Retrotransposon
1 million in genome
Linked to variety of disorders

32. Alu has inserted in NF-1 gene
Neurofibromatosis: autosomal dominant
Growth of nodules mainly affecting nerves in the skin

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

34. Now we must compare a Viral RNA with a Viral Retrotransposon

35. VIRAL RNA

36. Now a viral retrotransposon

37. Compare to the retrovirus
Here’s the Copia element of Drosophila
Similar gag and pol sequences
Compare to the retrovirus

38. Here’s the Ty element, again notice similarities to retroviruses
Delta sequences function like LTR’s in viruses

39. Summary Table Viral and non-viral Ty and Copia viral retrotransposons
Alu non viral retrotransposons

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

43. Blunt cut from donor

44. HUMAN
IMMUNODEFICIENCY
VIRUS
Human Helper T Lymphocyte