Generalized Transduction

• DNA bacterial viruses = bacteriophages normally replicate in cell, produce many copies of phage DNA, many copies of phage head coat proteins, finally assemble phage heads by packing phage DNA into new phage heads. Attach tail (if present), open cell, release progeny.
  View animation of phage infection
• Host DNA often degraded. But occasionally, piece of partially degraded bacterial DNA is correct size to be packed inside phage coat proteins, phage erroneously packs up a "mistake" = transducing phage.
  
  
  
  
• This "mistake" phage can't cause infection; but it can be transferred to a different bacterium, get DNA into cell without risk of being degraded in environment
• Even if this occurs, chances are slim that successful expression of DNA will occur --- still needs to undergo recombination. If most cells are killed by phage, not much use.
• E. coli phage P1 makes this DNA packing mistake about 1 in every 1000 phage particles. Astonishingly high error rate (relative to other phages). P1 can be used as very efficient way to move small pieces of DNA from one bacterium (donor) to another (recipient). Maximum size of DNA that can fit in phage head is only about 2% of bacterial chromosome.
• See diagram of transduction ("protected" image.) Why is this protected?

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