Bacterial genetics #2 Flashcards
Transposons a.k.a. transposable elements
pieces of DNA that can move around the genome and insert at target sites by transposition
~ major source of mutations e.g. gene knock-out
How do transposons move?
by excision and integration
or by replication
Insertion sequence (transposons)
bacterial DNA cut and paste element that codes for the enzyme needed for transposition, flanked by short inverted terminal repeats
Composite transposons
a pair of IS elements flank another gene and the whole segments acts as one transposable element
~ IS sequence may be inverted
Non-composite transposons
large and not dependent on IS-type elements
~ encode genes for transposition and drug resistance
~ start and end with terminal inverted repeats
Lysogens
bacterial strains with a prophage integrated into their genome
Prophage
when a phage is integrated into a bacterial genome
What happens when a mixed phage infects E.coli?
- an unstable transductant (double lysogen) = both types of DNA are expressed
- stable transductant produced by gene recombination
Autonomous transposon
encode the protiens needed to move the DNA
Non-autonomous transposons
rely on proteins made by autonomous element
DNA-only cut and paste transposons
an element bordered by short terminal inverted repeats (TIR) that are recognised by the element-encoded transposase
LTR element
long terminal repeat element
~ retrovirus
~ encodes several proteins including a reverse transcriptase
Non-LTR element
~ can be autonomous (LINE) or non-autonomous (SINE)
~ encode proteins with a range of functions
LINE
long Interspersed Elements
~ encode proteins that mediate their own transpotisiton
SINE
short Interspersed Elements
~ do not encode their proteins for their movement so rely on those from LINE
