Lecture 5 Flashcards
What are the 7 classes of transposable elements in bacteria?
Insertion sequences Tn3 family of transposons Tn7 transposon Gram positive transposons Transposable phages Inversion sequences
Explain the mechanism of Tn3 transposition
Replicative transposition.
Cointegrate formation, recombination then resolution catalysed by transposases and resolvase, respectively.
Give an example of a direct repair process and explain how it works
Photolyase system
What are the 6 repair mechanisms?
Photolyase repair Retrieval systems Tolerance systems SOS response Excision repair Mismatch repair
How is mismatch repair carried out?
UDG removes U from the nucleotide making an AP site. AP endonuclease makes a break in phosphodiester backbone adjacent to the AP site. DNA Pol I binds to the break and lays down new DNA. Gap sealed by DNA ligase
What is the mutS system?
Type of mismatch repair.
How does excision repair work?
Both long and short patch repair utilise the repair endonuclease encoded by uvrA, B and C genes
What are tolerance systems
Low fidelity DNA polymerase can synthesise new DNA past damaged bases
What are retrieval systems?
repair daughter strand gaps allows replication to occur successively without the use of a TSP. replies on other repair processes e.g. excision repair to repair the damage afterwards.
What does the SOS response do?
Allows cell to survive severe DNA damage by allowing cell to survive severe DNA damage by allowing DNA replication but at the expense of fidelity.
What protein are all genes/operons under SOS control under?
Subject to repression by LexA protein,
What does RecA do?
responds to DNA damage by changing conformation to RecA*
What does sulA do?
inhibit cell division
What are the controls of gene expression?
- Promoter recognition
- Promoter strength
- Alternative sigma factors
- Regulation of transcription initiation
What is promoter strength determined by?
Possession of 3 consensus elements:
- an up element
- a near -35 sequence
- a near -10 sequence
