Lecture 13 Flashcards
True or False
Transposons are the most common genes in nature
TRUE
What % of the human genome do transposons make up?
50%
How do transposons move relative to the host recombination system?
Transposons move from one site in the genome to another independent of host recombination system
What do transposons cause?
Large amounts of spontaneous mutations and chromosomal rearrangments
What do transposons allow?
The rapid acquisition of multiple antibiotic resistances and facilitates flow of genes between species
What are the types of Bacterial Transposons?
- Insertion sequences
- Composite transposons
- Non composite transposons
- Conjugative transposons
Describe an Insertion Sequence
They are the simplest type of transposon and only encode protein needed for their own transposition
What is at the end of all Insertion Sequences?
Ends of all IS show Inverted Terminal Repeats of 20-50 bp’s
Describe a Composite Transposon
- Consists of 2 IS elements either side of a central region carrying other genes e.g. antibiotic resistance
- Insertion Sequences elements supply transposase and Inverted Terminal Repeats
Describe Non-Composite Transposons
- They are simple
- Encode genes for own transposition and accessory functions, have inverted terminal repeats
Do Non-Composite Transposons rely on Insertion Sequences?
NO, they no not rely on Insertion Sequence modules for transposition
Which elements undergo conservative transposition?
Insertion Sequences and Composite Transposons
Describe Conservative transposition
‘Cut and Paste’
- Transposase makes two cuts
1. dsDNA cut in donor
2. Staggered cuts in target
What happens to the Donor DNA in conservative transposition?
- The donor DNA flanking sequence is either lost or repaired
- A small direct repeat of the target DNA (DNA surrounding where the element has been added ) either side of transposon
Describe Replicative transposition
‘Copy and Paste’
- Transposase make two cuts
1. 2x ssDNA cuts in donor
2. Staggered cuts in the target - Resolution of cointergrate requires resolvase
Which element undergo replicative transposition?
Non composite transposition
What is resolvase?
A site specific recombination enzyme which separates the two molecules through a recombination event
(replicative transposition)
What is a cointergrate?
Two molecules joined together, 2 copies of Transposon
What is the end results of replicative transposition?
Original DNA molecule reformed + new DNA molecule with transposon in it
Describe Conjugative transposons
- They are able to excise from genome and transpose from one cell to another via a conjugative intermediate
- They insert randomly into recipient and also reinsert into donor genome
What are Conjugative transposons important for?
Important in spreading of antibiotic resistance and virulence mainly in gram positive bacteria
Where do Conjugative transposons reside?
In bacterial chromosomes and carry lots of Antibiotic resistance
Do Conjugative transposons have an Ori T?
Yes
Can Conjugative transposons form a mating bridge?
Yes
How are insertions formed (when looking at transposons)?
Through transposition or homologous recombination
How are replicon fusions formed?
Through a process like Hfr formation
How are deletions formed?
Through homologous recombination between two copies of a transposon present in DIRECT orientation
->they are rearranged in the same reading direction
How are inversions formed?
Homologous recombination between two copies of a transposon present in inverted orientation
->read in opposite direction
