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Author(s): Serban L. Ilca [sup.1] , Xiaoyu Sun [sup.2] , Kamel El Omari [sup.3] , Abhay Kotecha [sup.1] [sup.4] , Felix de Haas [sup.4] , Frank DiMaio [sup.5] , Jonathan [...], Characterizing the genome of mature virions is pivotal to understanding the highly dynamic processes of virus assembly and infection. Owing to the different cellular fates of DNA and RNA, the life cycles of double-stranded (ds)DNA and dsRNA viruses are dissimilar. In terms of nucleic acid packing, dsDNA viruses, which lack genome segmentation and intra-capsid transcriptional machinery, predominantly display single-spooled genome organizations.sup.1-8. Because the release of dsRNA into the cytoplasm triggers host defence mechanisms.sup.9, dsRNA viruses retain their genomes within a core particle that contains the enzymes required for RNA replication and transcription.sup.10-12. The genomes of dsRNA viruses vary greatly in the degree of segmentation. In members of the Reoviridae family, genomes consist of 10-12 segments and exhibit a non-spooled arrangement mediated by RNA-dependent RNA polymerases.sup.11-14. However, whether this arrangement is a general feature of dsRNA viruses remains unknown. Here, using cryo-electron microscopy to resolve the dsRNA genome structure of the tri-segmented bacteriophage ɸ6 of the Cystoviridae family, we show that dsRNA viruses can adopt a dsDNA-like single-spooled genome organization. We find that in this group of viruses, RNA-dependent RNA polymerases do not direct genome ordering, and the dsRNA can adopt multiple conformations. We build a model that encompasses 90% of the genome, and use this to quantify variation in the packing density and to characterize the different liquid crystalline geometries that are exhibited by the tightly compacted nucleic acid. Our results demonstrate that the canonical model for the packing of dsDNA can be extended to dsRNA viruses. The cryo-electron microscopy structure of the bacteriophage ɸ6 dsRNA genome shows that the genome is packaged in a spooled manner that is more similar to dsDNA viruses than to other dsRNA viruses.

Negative-sense RNA viruses, such as influenza, encode large, multidomain RNA-dependent RNA polymerases that can both transcribe and replicate the viral RNA genome (1). In influenza virus, the polymerase (FluPol) is [...]

Author(s): Nicola G. A. Abrescia [1, 5]; Joseph J. B. Cockburn [1, 2, 5]; Jonathan M. Grimes [1]; Geoffrey C. Sutton [1]; Jonathan M. Diprose [1]; Sarah J. Butcher [3]; [...]

Author(s): Joseph J. B. Cockburn [1, 2]; Nicola G. A. Abrescia [1]; Jonathan M. Grimes [1]; Geoffrey C. Sutton [1]; Jonathan M. Diprose [1]; James M. Benevides [3]; George J. [...]

Author(s): Sarah J. Butcher [1, 2]; Jonathan M. Grimes [2, 3]; Eugeny V. Makeyev [1]; Dennis H. Bamford [1]; David I. Stuart (corresponding author) [3, 4] In most RNA viruses, [...]

Bluetongue virus (BTV) is a species of the Orbivirus within the Reoviradae group. X-ray crystallography has been used to determine the structure of the core particle of BTV. The atomic structure gives an insight into how around 1,000 protein components self-assemble using both the classical mechanism of quasi-equivalent contacts and geometrical quasi-equivalence.