Lecture 14 Flashcards
What does the phage lambda integration process require?
- attP site on the phage
- attB on the bacterial chromosome
- Phage intergrase
Describe the process of phage lambda integration
- Intergrase catalyses recombination between attB/P leading to integration of phage into the chromosome
- Two attachment sites form -> attL and attR (left and right), which are hybrids of B/P
- >this occurs once the phage is integrated - Once the phage is integrated it becomes a prophage and shuts of many genes
What does the phage lambda excision process require?
- phage L intergrase
- phage L excisionase
What are excisionase also called?
Recombination directionality factors (RDF)
What is a lysogen?
A bacterium with an integrated phage
What are the features of lysogenic conversion?
- Very efficient
- Doesn’t require cell to cell contact
- Incorporation not homology-dependent
True or False
Phage can survive harsh conditions that would eliminate bacteria i.e disinfectant or UV light
TRUE
What are genomic islands?
Discrete DNA segments that may be present in some but not all related strains
Where are genomic islands integrated in the chromosome?
Next to a tRNA gene
What do genomic islands have?
They are rich in A/T and have an intergrase gene
What is a pathogenicity island?
Elements that carry genes required for pathogenicity and virulence
What does pathogenicity refer to?
Ability to form disease
What does virulence refer to?
Extent of the disease caused by the bacterium
What are cargo genes?
They specify a phenotype, tends to be virulence or pathogenicity
Have most genomic islands lost mobility?
Yes, they have become fixed in the genome
Describe Integrative and Conjugative Elements
- Carry intergrase, excisionase, and conjugation genes
- Transfer by conjugation after excising from chromosome
- A copy of the ICE remains in the donor and the re-integrates
Finish the sentence
Integration of Integrative and Conjugative Elements is …
Highly specific in integration, occurring only at a few sites
Finish the sentence
Integration of Conjugative transposons is…
Random
Describe ICE integration and excision
(Same as phage lambda)
- ICE integrated between attL/R sites
- Recombination between L/R excises a circular island
- >gives attP (in ICE) and attB (in chromosome)
- ICE free cell can be recipient for conjugative transfer
- Recombination between attP/B results in integration
How do genetic islands aid in bacterial evolution?
Work as ‘fitness islands’ that adapt bacterium with a core chromosome to specific environmental niches
- > pathogenicity
- > resistance to antibiotics
- > symbiosis
- > xenobiotic degradation
