9HU6

Asymmetric unit from transcribing single-layered particle of bacteriophage phi6 in an over-expanded state

Summary for 9HU6

• Entry DOI: 10.2210/pdb9hu6/pdb
• EMDB information: 52401
• Descriptor: Major inner protein P1, NTPase (2 entities in total)
• Functional Keywords: cystovirus, phi6, semi-conservative transcription, cryo-em, cryogenic electron microscopy, localized reconstruction, symmetry relaxation, virus, dsrna virus, bacteriophage
• Biological source: Cystovirus phi6; More
• Total number of polymer chains: 3
• Total formula weight: 173701.23

Authors

Ilca, S.L.,Kumpula, E.-P.,Huiskonen, J.T. (deposition date: 2024-12-20, release date: 2026-01-14, Last modification date: 2026-02-04)

Primary citation

Ilca, S.L.,Sun, X.,Kumpula, E.P.,Eskelin, K.,Stuart, D.I.,Poranen, M.M.,Huiskonen, J.T.
Capsid restructuring activates semi-conservative dsRNA transcription in cystovirus ɸ6.
Mol.Cell, 86:289-, 2026

PubMed Abstract: Double-stranded (ds)RNA viruses replicate and transcribe their genome within a proteinaceous viral capsid to evade host cell defenses. While Reovirales members use conservative transcription, most dsRNA viruses, including cystoviruses, utilize semi-conservative transcription, in which a newly synthesized positive strand replaces the parental positive strand, which is released as mRNA. Here, we visualize semi-conservative transcription activation in cystovirus ɸ6 double-layered particles using cryogenic electron microscopy. We observe nucleotide-triggered disassembly of the domain-swapped outer capsid layer, subsequent expansion of the inner capsid layer, and stepwise assembly of transcription complexes at the opposing poles of the spooled dsRNA genome. These complexes consist of the viral polymerases embedded into a triskelion formed by the minor protein P7, which we show as essential for continuous transcription. The packaging hexamers proximal to the transcription sites channel the viral mRNA exit. Our results define the complex molecular pathway from the quiescent state to activated semi-conservative transcription.

PubMed: 41512857
DOI: 10.1016/j.molcel.2025.12.025

Experimental method

ELECTRON MICROSCOPY (3.5 Å)