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MBY364 Theme 3 summary
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Full summary of theme 3 (bacteriophage and cosmid vectors) made using lecture notes, the textbook and class notes.
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BACTERIOPHAGE AND COSMID VECTORSBACTERIOPHAGE λ
- Characteristics
- Is an extensively studied virus of E. coli
- Genetically complex
- Lambda DNA characteristics
- Linear duplex molecule (48.5kb) fully sequenced
- dsDNA
- Has short complimentary projections of 12nt at the 5’ ends -
single stranded
- Cohesive terminals associated to create cos sites
- Cohesive ends allow circularization of the DNA - crucial for integration
into bacterial genome
- Function of the cos sites
- Enable circularization of linear DNA - critical for lysogenic cycle
- λ DNA could be replicated by “rolling circle replication” - produces a
series of linear lambda genomes connected via the cos sites
- Cos sites are restricted by phage encoded endonucleases such that
single genomes are packaged
- Each copy is linked at a cos site
- Cos site serves as a recognition site for phage λ endonuclease A - releases
single copies for packaging per phage particle
- Functionally related genes are clustered together on the map
, INFECTION CYCLE OF PHAGE λ
- Phage λ is known as a temperate phage - can follow a lysogenic or lytic cycle
- Lytic cycle
- Phage DNA replication is followed directly by capsid protein synthesis
- Phage DNA are not stably maintained in the host cell
- Lysis of the host cell occurs followed by the release of infectious phage
particles
- Lysogenic cycle
- Phage DNA is stably maintained in host cell by incorporation in host
genome
- Integrated phage is called a pro-phage and the host cell is
physiologically indistinguishable
- Pro-phage is eventually released as an infectious phage particle by
following the lytic cycle
- Lysogen - a bacteria that contains an integrated copy of the phage genome
- Once a phage has infected a lysogen, it cannot be infected by another phage
- Lytic cycle is rapid with around 100 phages being released upon lysis
- Lysogenic phage is a bad vector
- Is integrated into the genome
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