Transposons are DNA sequences that can move within genomes. There are two main categories: DNA transposons, which use a cut-and-paste mechanism, and retrotransposons, which use a copy-and-paste mechanism. Barbara McClintock discovered the first transposable element in maize in the 1940s. DNA transposons have been found in bacteria and eukaryotes, while retrotransposons are more common in eukaryotes. Retrotransposons include LTR retrotransposons and non-LTR retrotransposons such as LINEs and SINEs, which account for a large percentage of the human genome. Transposition mechanisms involve RNA transcription, reverse

1. Transposon and Mechanisms of Transposition

2. Transposon
 DNA sequence that can move in the genome
 Also called mobile DNA element or transposable element
 “selfish DNA”--exist only to maintain themselves ?
 Transposition: The process by which these sequences are
copied and inserted into a new site in the genome
 Probably had a significant influence on evolution

3. How transposon was found
 1940s, Barbara McClintock discovered the
first transposable element in maize, earned a
Nobel prize in 1983.
Late 1960s, transposition was also found in
Bacteria.
Barbara McClintock

4. Two Categories
 DNA transposons
 Retrotransposons
“cut-and-paste”
 Most mobile elements in bacteria is
DNA transposons
 In contrast, most mobile elements
in eukaryotes are retrotransposons,
but eukaryotic DNA transposons
also occur.
“copy-and-paste”

5. DNA transposons
General structure of bacterial IS elements
 Bacterial Insertion Sequences
(IS element)
 P element in Drosophila

6. General process of transposition
for DNA transposons

7. General structure of eukaryotic LTR retrotransposons
Retrotransposons
 LTR retrotransposons:
 Non-LTR retrotransposons: the most common type of transposons in mammals
What is the difference from retrovirus?

8. Generation of RNA from LTR transposon

9. Model for reverse transcription

10. Retrotransposons
• Non-LTR retrotransposons
 long interspersed elements (LINEs)
≈6 kb in human
account for 21% of the genome
 short interspersed elements (SINEs)
≈300 bp in human
account for 13% of the genome

11. General Principles of LINE transposition

12. SINEs
(Short Interspersed Elements)

13.  Most are tRNA derived; Alu is 7SL-RNA
 Nonautonomous
 Dependent on other machinery- genome
“parasite”
 RNA Pol III
 Needs LINE Endonuclease and Reverse
Transcriptase for activity

14.  Average size 150-200 base pairs
 Composed of 3 parts
 5’ head
 Body
 3’ tail

17. Transport

21.  Where there is a SINE, there is a LINE
 Specificity of EN/RT of LINE dictates
location
 Expressed during early embryogenesis and
decreases in development
 Active in tumor cells
 Integrates into germ lines

22. Thank you