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Lambda excision revisited: testing a model for synapsis of prophage ends.
1Department of Microbiology, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA. martin.pato@uchsc.edu
Journal of Bacteriology
|August 8, 2001
Summary
Bacteriophage lambda excision occurs rapidly even without DNA replication. Supplying additional Int protein or lowering temperature post-induction shows replication is not required for rapid excision, contradicting prior models.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- Bacteriophage lambda excision is a critical step in its lytic and lysogenic cycles.
- A proposed model suggests prophage DNA replication facilitates end synapsis for efficient excision.
- This model posits that replication forks are held together, spooling DNA and drawing ends together.
Purpose of the Study:
- To reexamine bacteriophage lambda prophage excision.
- To test a model proposing in situ prophage replication is necessary for end synapsis and excision.
- To investigate factors influencing the rate of prophage excision.
Main Methods:
- Thermoinduction of lambda prophage in Escherichia coli.
- Inhibition of in situ lambda replication.
- Supplementation with additional Int protein.
- Temperature shift experiments post-induction.
Main Results:
- A nonreplicating prophage showed a significantly reduced excision rate after thermoinduction, consistent with the model.
- Rapid excision was observed when additional Int protein was supplied.
- Rapid excision also occurred when the temperature was reduced after induction.
- These results indicate Int protein is partially thermosensitive at 42°C.
Conclusions:
- In situ lambda replication is not a prerequisite for rapid prophage excision.
- The observed rapid excision under specific conditions contradicts the proposed model.
- Bacteriophage lambda excision can occur independently of its replication machinery.