Transposon and Mechanisms of Transposition
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
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
http://en.wikipedia.org/wiki/Barbara_McClintock
Two Categories
 DNA transposons
 Retrotransposons
“cut-and-paste”
“copy-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.
Lodish et al., Molecular Cell Biology, 7th ed. Fig 10-8
DNA transposons
 Bacterial Insertion Sequences (IS element)
 P element in Drosophila
General structure of bacterial IS elements
Lodish et al., Molecular Cell Biology, 7th ed. Fig 10-9
General process of transposition
for DNA transposons
Lodish et al., Molecular Cell Biology, 7th ed. Fig 10-10
Retrotransposons
 LTR retrotransposons:
 Non-LTR retrotransposons: the most common type of transposons in mammals
General structure of eukaryotic LTR retrotransposons
Lodish et al., Molecular Cell Biology, 7th ed. Fig 10-11
What is the difference from retrovirus?
Generation of RNA from LTR transposon
Lodish et al., Molecular Cell Biology, 7th ed. Fig 10-12
Model for reverse transcription
Lodish et al., Molecular Cell Biology, 7th ed. Fig 10-13
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
Lodish et al., Molecular Cell Biology, 7th ed. Fig 10-15
General Principles of LINE transposition
Lodish et al., Molecular Cell Biology, 7th ed. Fig 10-16
SINEs
(Short Interspersed Elements)
Weiner (2000) Fig 1
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
Average size 150-200 base pairs
Composed of 3 parts
 5’ head
 Body
 3’ tail
Vassetzky (2013)
http://biol.lf1.cuni.cz/ucebnice/images/rep1.gif
Kramerov & Vassetzky (2005)
Transport
Kramerov & Vassetzky (2005)
Batzer & Deininger, Nature Reviews
Genetics (2002) Box 1
Kramerov & Vassetzky (2005)
“Transposons: Mobile DNA” (2012)
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
References
Batzer, M.A. & Deininger, P.L. Alu repeats and Human genomic diversity. Nature Reviews Genetics 3,
370-379 (2002). Doi:10.1038/nrg798
http://www.nature.com/nrg/journal/v3/n5/box/nrg798_BX1.html
Kramerov, D.A. & Vassetzky, N.S. Short Retroposons in Eukaryotic Genomes. International Review of
Cytology, vol 247 (2005) doi: 10.1016/S0074-7696/05
Lodish et al., Molecular Cell Biology, 7th ed.
“Transposons: Mobile DNA”. (2012)
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Transposons.html
Vassetzky. SINEBase (2013) http://sines.eimb.ru
Weiner, A. Do all SINEs lead to LINEs? Nature Genetics 24, 332-333 (2000) doi:10.1038/74135
http://www.nature.com/ng/journal/v24/n4/full/ng0400_332.html