Transposable Elements
fragment of DNA that can be excised and then moved elsewhere
Genetic elements that move are called: (5)
- controlling elements
- jumping genes
- mobile genes
- mobile genetic elements
- transposons
Barbara McClintock (1902-1992)
- discovered TEs in 1940/50s
- ignored for 20 years because…
1. it was too different
2. didn’t fit w the accepted understanding of the genome
3. other scientists didn’t understand
4. it was the 1950s and she was a women - her work eventually recognized w a Nobel prize in physiology in 1983
2 genetic factors that are required for chromosome breakage (in maize):
- dissociation factors (DS): always at site of breakage (cis factor)
- activator factor (Ac): at an unlinked locus, but was required to activate or cause breakage (trans factor)
Ac factor is considered
mobile (& resides in different location in different individual plants)
Abrupt changes associated with the activity of Ac and DS factors were given the name
controlling elements
Transposase
an enzyme that has a “cut and paste” mechanism that removes the DNA element from one locus and inserts it into another
Mechanism of transposition (3 steps)
- transpose makes a staggered cut in the host DNA molecule (creates overhang)
- transposon inserts between ends of cut
- host DNA repair machinery joins host DNA & transposon at each end using overhangs as templates
Ds is _______ in the absence of a func. Ac
stable
Ac is….
unstable
Ds is a _________ variant of Ac
deletion
Ac
autonomous element (encodes all info necessary for movement)
- transposase & IR = inverted repeats
Ds
non-autonomous element (requires a related autonomous element to move)
- no transposase
Class 1: retrotransposons
- related to retrovirus
- use an RNA intermediate
- they encode a reverse transcriptase that makes a DNA copy of the RNA that can be encoded into the genome
- found in eukaryotes only
Class 2: DNA transposons
- DNA element that moves directly from one position in genome to another (cut & paste)
or may be copied & moved as a DNA molecule - found in both eukaryotes and prokaryotes
Common characteristics of TEs
- have direct repeats - short repeated seq flanking the element (arise by transposition)
- carry a gene coding for an enzyme that catalyzes transposition
1. transposase: elements use DNA intermediate
2. reverse transcriptase: elements use RNA intermediate
Retrovirus
single-stranded virus, uses a double stranded DNA intermediate for replication
Retroviral genes
gag, pol, env
genes encoding proteins required for transposition
Gag
maturation of viral RNA genome
Pol
reverse transcriptase + integrase
Env
structural protein surrounding virus
LTR
long terminal repeat; recognition site for transposition
How do TEs cause mutations
- insert themselves in coding regions & disrupt protein func
- when DNA transposons move = cause a deletion or DSB
TEs can ______ gene expression by influencing….
increase, neighbouring promotor or replacing nascent promotor
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Module 413
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Module 5 - Part 112
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Module 5 - Part 219
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Module 6 - Part 17
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Module 6 - Part 214
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Module 1 - Part 118
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Module 1 - Part 211
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Module 2 - Part 113
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Module 2 - Part 210
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Module 3 - Part 16
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Module 3 - Part 215
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Module 7 - Part 118
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Module 7 - Part 26
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Module 8 - Part 112
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Module 8 - Part 219
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Module 9 - Part 117
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Module 9 - Part 244
