Self-assembly of double-stranded RNA bacteriophages

Area of Science:

• Virology
• Structural Biology
• Molecular Biology

Background:

• Double-stranded RNA (dsRNA) viruses in the Cystoviridae family infect bacteria.
• Bacteriophage phi6 is a model dsRNA virus with similarities to eukaryotic dsRNA viruses.
• Phi6 virion assembly involves procapsid formation, genome encapsidation, nucleocapsid shell assembly, and envelope formation.

Purpose of the Study:

• To review the procapsid and nucleocapsid assembly of bacteriophage phi6 using in vitro systems.
• To elucidate the roles of viral enzymes and proteins in dsRNA virus assembly.
• To explore common assembly mechanisms across different dsRNA viruses.

Main Methods:

• Establishment and utilization of in vitro assembly systems for bacteriophage phi6.
• Analysis of assembly intermediates and conformational changes.
• Characterization of essential viral enzymes (P4, P2) and proteins (P1, P8) in the assembly process.

Main Results:

• In vitro systems revealed essential roles for packaging NTPase (P4) and RNA-dependent RNA polymerase (P2) in nucleation.
• Procapsid assembly involves major procapsid protein (P1) tetramers stabilized by P4, with associated polypeptide folding.
• In vitro assembled procapsids selectively package and replicate genomic ssRNA.
• Infectious nucleocapsids were assembled in vitro, with nucleocapsid coat protein (P8) assembling around the polymerase complex in a template-assisted manner.

Conclusions:

• In vitro assembly systems are powerful tools for studying dsRNA virus assembly mechanisms.
• Specific viral proteins and enzymes are critical for initiating and completing the assembly of the phi6 virion.
• Findings provide insights into conserved assembly principles applicable to other dsRNA viruses.