Lambda excision revisited: testing a model for synapsis of prophage ends

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.