Bacterial Phages

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Bacterial Phages

• Classification
• Lytic life cycle
• Applications
• Phage therapy
• Phage display
• Protein expression
• General transduction

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Classification of Phages

• dsDNA phages
• T4, T7, Mu, P1, P2, P4, P22, lambda
• ssDNA phages
• F1, M13
• dsRNA phages
• Phi6
• ssRNA phages
• MS2

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Gene Regulation in Phages

• Early events
• Host proteins help transcribe the phage genes
• e.g. regulatory factor or specific phage RNA
  polymerase
• Expression of early genes
• DNA polymerase, ligase, primase, helicase
• Stop protein synthesis of host cells
• Activation of late genes
• Proteins for phage head, tail and DNA packaging

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Potential ApplicationsPhage Therapy

• Use phage as antibiotic
• Idea was conceived immediately after discovery of
  phages
• Rational
• Phage will not infect eukaryotic cells
• Phages will replicate themselves
• Potential use in animals.

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Potential Applications
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Potential ApplicationsPhage Display

• Use phage in search for protein-protein
  interaction
• Rational
• Large population
• Replacement of surface proteins with target
  proteins
• M13 phages
• Filamentous
• Adsorb to pilus
• Does not lyse cells

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Potential Applications General Transduction

• Definition
• Phage-mediated DNA transfer from one bacterium to
  another
• Requirement
• Host-DNA has to be disrupted but not completely
  degraded.
• DNA packaging is not specific
• Phage P1 (for E. coli) and P22 (for salmonella
  typhimurium)

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