Transcriptional regulation
Learning outcomes:
1. Introduction to bacteriophage
2. Types of bacteriophage life cycle
3. Bacteriophage lambda
4. Transcriptional regulation/ switches of phage λ life cycles
5. Overview to the phage practical
Introduction
• Bacteriophage or phage = bacteria viruses
• 3 major morphological classes:
1. Icosahedral tailless: X174
2. icosahedral tailed: T4, T7, λ
3. filamentous: M13
• bacteriophage= double stranded DNA viruses
• viral genome usually linear when packaged
• head/caspid = made out of protein & DNA packaged
• Tail like structure surrounded by fibrous protein that allow the tail region to be contracted.
• baseplate= attached to surface of bacterium
How do bacteriophage infect their host?
• T-even phages inject their DNA into bacterial cells
• T-even phage = E.coli phage = double-stranded bacteriophage
1. Bind through tail fiber to the bacterial outer cell wall
2. Contract tail region to push needle structure through the bacteria cell wall
1. Aided by a lysozyme protein in the bacteriophage head
2. Lysozyme protein breaks down bacterial cell wall
3. Phage encoded lysozyme injects and digests through the bacterial cell wall
4. Further contraction by bacteriophage injects DNA into cytoplasm of bacterium
,What happens when the DNA from bacteriophage enters the bacterium?
• What happens next depends on 2 different sets of transcriptional programmes
• The cycle the phage enters is a transcriptional decision based on phage genes
• Lytic cycle results in the lysis of the host
• Lytic cycle:
1. After injection of linear phage genome into host
2. Transcription – translation – replication phage genome
3. Generate hundreds of bacteriophage copies
- 1 phage particle per 1 genome replication
4. Assemble and package new phage
5. Phage lysis host
6. Bacteriophage released into environment
7. Bacterium dead
• Lysogenic cycle
Repression- integration- cellular reproduction- induction
- Only 1 transcriptional cycle
, - Phage genome circularises
- Circular genome integrates into host genome
Latense/ Silent stage
Does not affect bacterium
Exist in prophage
Prophage can be induced to exercise and enter the lytic sycle
- Bacteria fairly propagates (grow)
- Every time bacteria divides, phage genome enters the new bacterial cells and copied along
host genome
How genetic switch work in 1 transcriptional regulatory region within the bacteriophage genome to
dictate the 2 possible outcomes (lytic or lysogenic cycle)
• Bacteriophage evolved a similar mechanism for regulating transcription of
genes to prokaryotic bacterial host.
Lytic development:
• Phage infective cycle is divided into early (before replication) and late (after
replication) development
• Early development
- Phage devote early development into synthesising phage genes required for DNA replication
Learning outcomes:
1. Introduction to bacteriophage
2. Types of bacteriophage life cycle
3. Bacteriophage lambda
4. Transcriptional regulation/ switches of phage λ life cycles
5. Overview to the phage practical
Introduction
• Bacteriophage or phage = bacteria viruses
• 3 major morphological classes:
1. Icosahedral tailless: X174
2. icosahedral tailed: T4, T7, λ
3. filamentous: M13
• bacteriophage= double stranded DNA viruses
• viral genome usually linear when packaged
• head/caspid = made out of protein & DNA packaged
• Tail like structure surrounded by fibrous protein that allow the tail region to be contracted.
• baseplate= attached to surface of bacterium
How do bacteriophage infect their host?
• T-even phages inject their DNA into bacterial cells
• T-even phage = E.coli phage = double-stranded bacteriophage
1. Bind through tail fiber to the bacterial outer cell wall
2. Contract tail region to push needle structure through the bacteria cell wall
1. Aided by a lysozyme protein in the bacteriophage head
2. Lysozyme protein breaks down bacterial cell wall
3. Phage encoded lysozyme injects and digests through the bacterial cell wall
4. Further contraction by bacteriophage injects DNA into cytoplasm of bacterium
,What happens when the DNA from bacteriophage enters the bacterium?
• What happens next depends on 2 different sets of transcriptional programmes
• The cycle the phage enters is a transcriptional decision based on phage genes
• Lytic cycle results in the lysis of the host
• Lytic cycle:
1. After injection of linear phage genome into host
2. Transcription – translation – replication phage genome
3. Generate hundreds of bacteriophage copies
- 1 phage particle per 1 genome replication
4. Assemble and package new phage
5. Phage lysis host
6. Bacteriophage released into environment
7. Bacterium dead
• Lysogenic cycle
Repression- integration- cellular reproduction- induction
- Only 1 transcriptional cycle
, - Phage genome circularises
- Circular genome integrates into host genome
Latense/ Silent stage
Does not affect bacterium
Exist in prophage
Prophage can be induced to exercise and enter the lytic sycle
- Bacteria fairly propagates (grow)
- Every time bacteria divides, phage genome enters the new bacterial cells and copied along
host genome
How genetic switch work in 1 transcriptional regulatory region within the bacteriophage genome to
dictate the 2 possible outcomes (lytic or lysogenic cycle)
• Bacteriophage evolved a similar mechanism for regulating transcription of
genes to prokaryotic bacterial host.
Lytic development:
• Phage infective cycle is divided into early (before replication) and late (after
replication) development
• Early development
- Phage devote early development into synthesising phage genes required for DNA replication
