The Nature of Transposons Chapter 11 pp 300-315

1. The Nature of TransposonsChapter 11pp 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 Cut and Paste Copy and Paste 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. Staggered cut Direct repeats are generated

11. 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. Dr. Barbara McClintock 1902-1992 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. 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. 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. General Mechanism Of Retrotransposons Note: retrotransposons are not found in prokaryotes

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

30. Non-viral Retrotransposons Humans Non-Viral SINES LINES 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. 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 Ty and Copia viral retrotransposons Viral and non-viral 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