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

Lodish et al., Molecular Cell Biology, 7th ed. Fig 10-8

DNA transposons Retrotransposons

“cut-and-paste”

Most mobile elements in bacteriabacteria is DNA transposons

In contrast, most mobile elements in eukaryoteseukaryotes are retrotransposons, but eukaryotic DNA transposons also occur.

“copy-and-paste”

DNA transposons

General structure of bacterial IS elementsLodish et al., Molecular Cell Biology, 7th ed. Fig 10-9

Bacterial Insertion Sequences (IS element)

P element in Drosophila

Lodish et al., Molecular Cell Biology, 7th ed. Fig 10-10

General process of transposition for DNA transposons

General structure of eukaryotic LTR retrotransposonsLodish et al., Molecular Cell Biology, 7th ed. Fig 10-11

Retrotransposons LTR retrotransposons:

Non-LTR retrotransposons: the most common type of transposons in mammals

What is the difference from retrovirus?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 transcriptionLodish et al., Molecular Cell Biology, 7th ed. Fig 10-13

Retrotransposons Non-LTR retrotransposonsNon-LTR retrotransposons long interspersed elements (LINEsLINEs)

≈6 kb in human

account for 21% of the genome

short interspersed elements (SINEsSINEs)

≈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-RNANonautonomousDependent on other machinery- genome “parasite” RNA Pol IIINeeds 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 LINESpecificity of EN/RT of LINE dictates locationExpressed during early embryogenesis and decreases in developmentActive in tumor cellsIntegrates 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:10.1038/74135http://www.nature.com/ng/journal/v24/n4/full/ng0400_332.html