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Architectural flexibility in lambda site-specific recombination: three alternate conformations channel the attL site
1Laboratory of Molecular Biology, National Institute of Mental Health, Bethesda, MD 20892-4034, USA. asegall@sunstroke.sdsu.edu
Summary
Bacteriophage lambda Integrase (Int) protein mediates recombination between attL sites. Integration Host Factor (IHF) protein stimulates this in vivo but not in vitro, revealing a unique pathway dependent on attL architecture.
Area of Science:
- Molecular Biology
- Genetics
- Virology
Background:
- Phage lambda Integrase (Int) protein mediates DNA recombination in integration (attP/attB) and excision (attL/attR).
- Recombination between identical attL sites is inefficiently mediated by Int alone, with Integration Host Factor (IHF) stimulating it in vivo but not in vitro.
Purpose of the Study:
- To investigate the in vitro recombination between two attL sites mediated by Int and IHF.
- To elucidate the unique requirements and mechanisms of this alternative recombination pathway.
Main Methods:
- In vitro and in vivo recombination assays using modified attL substrates.
- Analysis of mutant Int proteins and intracellular plasmids.
Main Results:
- IHF stimulates in vitro recombination between attL sites lacking the P'1 Int binding site, achieving efficiencies comparable to in vivo levels.
- This IHF-stimulated recombination pathway exhibits distinct requirements compared to other lambda recombination pathways.
Conclusions:
- A unique attL architecture requiring IHF-mediated DNA bending and inhibition by Int at the P'1 site characterizes this pathway.
- This pathway demonstrates the flexibility of the lambda recombination system and aids in separating strand exchange chemistry from directionality determinants.