The terminase of bacteriophage lambda. Functional domains for cosB binding and multimer assembly

Area of Science:

• Molecular Biology
• Virology
• Genetics

Background:

• Terminase is a protein complex essential for lambda DNA packaging, comprising gpNul and gpA subunits.
• Bacteriophages lambda and 21 possess distinct terminases with specificities in DNA and prohead binding, and their subunits are not interchangeable.
• Recombination can generate lambda-21 hybrid phages with hybrid terminase genes, offering a tool to study functional domains.

Purpose of the Study:

• To identify functional domains of terminase by analyzing lambda-21 hybrid phages with hybrid terminase genes.
• To compare the packaging specificities and gene structures of hybrid phages to map functional domains.
• To elucidate the roles of specific terminase subunit portions in DNA binding, prohead binding, and multimer formation.

Main Methods:

• Construction and analysis of lambda-21 hybrid phages with recombined terminase genes.
• In vivo packaging specificity determination using complementation tests and helper packaging experiments.
• Genetic mapping via restriction enzyme site mapping and DNA sequencing to locate crossover sites.

Main Results:

• Hybrid phage 51, with a lambda A gene and a hybrid 1/Nul gene, demonstrated that the amino-terminal gpNul portion binds 21 DNA and the carboxy-terminal portion interacts with gpA.
• Hybrid phage 54, with a hybrid 2/A gene, showed that the amino-terminal gpA portion forms functional multimers with gp1 (implying interaction with gpNul).
• These findings pinpointed three distinct functional domains within the terminase complex.

Conclusions:

• The amino-terminal part of gpNul is crucial for DNA binding.
• The carboxy-terminal part of gpNul is essential for interaction with gpA.
• The amino-terminal part of gpA is involved in interaction with gpNul, contributing to the overall functional architecture of terminase.