Capsid restructuring activates semi-conservative dsRNA transcription in cystovirus ɸ6

Area of Science:

• Virology
• Molecular Biology
• Structural Biology

Background:

• Double-stranded (ds)RNA viruses replicate within protective capsids, evading host defenses.
• Most dsRNA viruses, unlike Reovirales, use semi-conservative transcription for genome replication.
• Cystoviruses employ semi-conservative transcription, releasing the parental positive strand as mRNA.

Purpose of the Study:

• To visualize the activation of semi-conservative transcription in cystovirus ɸ6.
• To elucidate the molecular mechanisms underlying transcription initiation and elongation.
• To identify key viral proteins involved in the transcription process.

Main Methods:

• Cryogenic electron microscopy (cryo-EM) was used to visualize double-layered particles of cystovirus ɸ6.
• Observation of nucleotide-triggered structural changes in the viral capsid.
• Analysis of transcription complex formation and associated viral proteins.

Main Results:

• Nucleotide binding triggers disassembly of the outer capsid layer and expansion of the inner capsid.
• Transcription complexes assemble at the poles of the spooled dsRNA genome.
• Viral polymerases, complexed with minor protein P7, are essential for continuous transcription, with packaging hexamers facilitating mRNA export.

Conclusions:

• The study defines the molecular pathway for semi-conservative transcription activation in cystovirus ɸ6.
• Protein P7 and packaging hexamers play critical roles in viral RNA synthesis and export.
• Visualizing these dynamic processes provides insights into dsRNA virus replication strategies.