A structural model of the genome packaging process in a membrane-containing double stranded DNA virus

Area of Science:

• Structural Biology
• Virology
• Molecular Biology

Background:

• Viral genome encapsidation and exit are critical for infection.
• Icosahedral viruses typically use a unique vertex for genome translocation.
• Membrane-containing viruses face additional complexity in genome transport through lipid bilayers.

Purpose of the Study:

• To determine the structure of the genome packaging complex and membrane conduit in bacteriophage PRD1.
• To elucidate the mechanism of viral genome encapsidation in membrane-containing viruses.

Main Methods:

• Single particle electron cryo-microscopy (cryo-EM)
• Symmetry-free image reconstruction
• Structural analysis of virion, procapsid, and mutant particles

Main Results:

• The packaging complex at the unique vertex of PRD1 crosses the lipid bilayer.
• A dodecameric portal complex (P9 and P6) and a transmembrane hexamer (P20/P22) form the membrane conduit.
• The genome terminal protein P8 acts as a valve to seal the channel after packaging.

Conclusions:

• The PRD1 packaging complex facilitates DNA translocation through the viral membrane.
• A proposed assembly pathway for the genome packaging apparatus is presented.
• Structural insights into viral genome packaging mechanisms are provided.