Learning Objective
Explain the mechanism and requirements of homologous recombination in bacteria, including the role of exogenotes, recombination enzymes (especially recA), and the importance of homology in stabilizing imported linear DNA.
Homologous recombination is the primary mechanism that stabilizes foreign linear DNA entering a bacterial cell via transformation, conjugation, or transduction.
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Key Concepts
- Imported DNA enters the cell as short linear fragments called exogenotes.
- Linear DNA is unstable and rapidly degraded by exonucleases unless it recombines.
- Homologous recombination causes an exchange between:
- the exogenote (linear) DNA and
- a homologous region on the circular bacterial chromosome.
- Requires several genes’ worth of sequence homology (not just a few base pairs).
- Requires a set of recombination genes:
- recA → essential
- recB, recC, recD → supporting recombination enzymes
- End result: the foreign DNA is permanently integrated, replacing the homologous segment on the chromosome.
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