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Bacteriophage lambda DNA packaging: scanning for the terminal cohesive end site during packaging.
Summary
Bacteriophage lambda terminase poorly packages phage 21 DNA due to a binding defect at the cos phi 21 site. This interaction failure prevents efficient DNA packaging, highlighting the specificity of phage DNA packaging mechanisms.
Area of Science:
- Molecular Biology
- Virology
- Genetics
Background:
- Bacteriophage lambda exhibits poor packaging of related phage 21 DNA.
- The cohesive end site (cos) is crucial for phage DNA packaging specificity.
Purpose of the Study:
- Investigate the interaction between phage lambda terminase and the cohesive end site of phage 21 (cos phi 21).
- Determine the molecular basis for the packaging defect of phage 21 DNA by phage lambda.
Main Methods:
- In vitro cleavage assays of cos phi 21 by lambda terminase.
- In vitro packaging experiments to assess packaging specificity.
- Competition experiments to analyze terminase-cos binding interactions.
Main Results:
- Lambda terminase cleaved cos phi 21 at only 1% of the efficiency of cos lambda.
- In vitro packaging confirmed the in vivo observed packaging specificities for lambda and 21.
- Competition experiments revealed that cos phi 21 fails to bind lambda terminase.
Conclusions:
- The packaging defect is due to the inability of cos phi 21 to bind lambda terminase.
- Terminase binding to cos requires interactions outside the central symmetry region.
- The cos site likely involves adjacent binding and nicking sites for terminase.