Summary information and primary citation
- PDB-id
- 5tc1; SNAP-derived features in text and JSON formats;
DNAproDB
- Class
- viral protein-RNA
- Method
- cryo-EM (3.6 Å)
- Summary
- In situ structures of the genome and genome-delivery apparatus in ssrna bacteriophage ms2
- Reference
- Dai X, Li Z, Lai M, Shu S, Du Y, Zhou ZH, Sun R (2017): "In situ structures of the genome and genome-delivery apparatus in a single-stranded RNA virus." Nature, 541, 112-116. doi: 10.1038/nature20589.
- Abstract
- Packaging of the genome into a protein capsid and its subsequent delivery into a host cell are two fundamental processes in the life cycle of a virus. Unlike double-stranded DNA viruses, which pump their genome into a preformed capsid, single-stranded RNA (ssRNA) viruses, such as bacteriophage MS2, co-assemble their capsid with the genome; however, the structural basis of this co-assembly is poorly understood. MS2 infects Escherichia coli via the host 'sex pilus' (F-pilus); it was the first fully sequenced organism and is a model system for studies of translational gene regulation, RNA-protein interactions, and RNA virus assembly. Its positive-sense ssRNA genome of 3,569 bases is enclosed in a capsid with one maturation protein monomer and 89 coat protein dimers arranged in a T = 3 icosahedral lattice. The maturation protein is responsible for attaching the virus to an F-pilus and delivering the viral genome into the host during infection, but how the genome is organized and delivered is not known. Here we describe the MS2 structure at 3.6 Å resolution, determined by electron-counting cryo-electron microscopy (cryoEM) and asymmetric reconstruction. We traced approximately 80% of the backbone of the viral genome, built atomic models for 16 RNA stem-loops, and identified three conserved motifs of RNA-coat protein interactions among 15 of these stem-loops with diverse sequences. The stem-loop at the 3' end of the genome interacts extensively with the maturation protein, which, with just a six-helix bundle and a six-stranded β-sheet, forms a genome-delivery apparatus and joins 89 coat protein dimers to form a capsid. This atomic description of genome-capsid interactions in a spherical ssRNA virus provides insight into genome delivery via the host sex pilus and mechanisms underlying ssRNA-capsid co-assembly, and inspires speculation about the links between nucleoprotein complexes and the origins of viruses.
