9I7W

Extended and wrapped protein P7 dimers of dimers, the P1 layer and the RNA-dependent RNA polymerase P2 in transcribing particles of bacteriophage phi6

Summary for 9I7W

• Entry DOI: 10.2210/pdb9i7w/pdb
• Related: 1HHT 9HTW 9I5C
• EMDB information: 52389
• Descriptor: DNA (5'-D(*TP*TP*TP*CP*C)-3'), RNA-directed RNA polymerase, Nucleocapsid protein, ... (4 entities in total)
• Functional Keywords: inner protein capsid, transcribing phi6 particle, localized reconstruction, viral protein
• Biological source: Cystovirus phi6; More
• Total number of polymer chains: 14
• Total formula weight: 511626.34

Authors

Kumpula, E.-P.,Ilca, S.L.,Huiskonen, J.T. (deposition date: 2025-02-03, release date: 2026-01-21)

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, 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 (4.8 Å)