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Bacteriophage P2 and P4 morphogenesis: identification and characterization of the portal protein
S Rishovd1, O J Marvik, E Jacobsen
1Institute of Biology, University of Oslo, Norway.
Abstract:
The portal structure has been implicated in several aspects of the bacteriophage life cycle, including capsid assembly initiation and DNA packaging. Here we present evidence that P2 gene Q codes for the P2 and P4 portal protein. First, microsequencing shows that capsid protein h6 is derived from gpQ, most probably by proteolytic cleavage. Second, antibodies against gpQ bind to the portal structure in disrupted P2 phage virions, as observed by electron microscopy. Third, gpQ partially purified from an overexpressing plasmid assembles into portal-like structures. We also show by microsequencing that capsid protein h7 is encoded by the P2 scaffold gene, O, and is probably derived from gpO by proteolytic cleavage. Previous work has demonstrated processing of the major capsid protein. Thus, all essential capsid proteins of P2 and P4 are proteolytically cleaved during the morphogenetic process.
Insights
The P2 gene Q protein is identified as the portal protein in bacteriophage P2 and P4. This protein is crucial for capsid assembly and DNA packaging during phage replication.
Area of Science:
- Microbiology
- Molecular Biology
- Structural Biology
Background:
- The portal structure is essential for bacteriophage (phage) life cycle stages, including capsid assembly and DNA packaging.
- Bacteriophage P2 and P4 share structural and functional similarities in their portal proteins.
Purpose of the Study:
- To identify the specific gene encoding the portal protein in bacteriophages P2 and P4.
- To elucidate the role of gene products in phage morphogenesis and capsid formation.
Main Methods:
- Microsequencing of capsid proteins to determine their origin.
- Immunoelectron microscopy using antibodies against gene products.
- In vitro assembly of purified proteins into portal-like structures.
Main Results:
- Gene Q (gpQ) encodes the portal protein for both P2 and P4 bacteriophages.
- Capsid protein h6 is derived from gpQ via proteolytic cleavage.
- Capsid protein h7 is derived from the P2 scaffold gene O (gpO) via proteolytic cleavage.
- Purified gpQ can self-assemble into portal-like structures.
Conclusions:
- All essential capsid proteins of bacteriophages P2 and P4 undergo proteolytic cleavage during morphogenesis.
- Gene Q is definitively identified as the structural gene for the portal protein in P2 and P4 phages.
- This cleavage processing is a critical step in the assembly of infectious phage particles.