The ϕ6 cystovirus protein P7 becomes accessible to antibodies in the transcribing nucleocapsid: a probe for viral structural elements

RNA Packaging in the Cystovirus Bacteriophages: Dynamic Interactions during Capsid Maturation

The bacteriophage family Cystoviridae consists of a single genus, Cystovirus, that is lipid-containing with three double-stranded RNA (ds-RNA) genome segments. With regard to the segmented dsRNA genome, they resemble the family Reoviridae. Therefore, the Cystoviruses have long served as a simple model for reovirus assembly. This review focuses on important developments in the study of the RNA packaging and replication mechanisms, emphasizing the structural conformations and dynamic changes during maturation of the five proteins required for viral RNA synthesis, P1, P2, P4, P7, and P8. Together these proteins constitute the procapsid/polymerase complex (PC) and nucleocapsid (NC) of the Cystoviruses. During viral assembly and RNA packaging, the five proteins must function in a coordinated fashion as the PC and NC undergo expansion with significant position translation. The review emphasizes this facet of the viral assembly process and speculates on areas suggestive of additional research efforts.

Heteroaggregation of an enveloped bacteriophage with colloidal sediments and effect on virus viability

Four sediments in the colloidal size range: goethite, montmorillonite, illite, and kaolinite, were suspended with the bacteriophage φ6, a model enveloped virus, to determine relative rates of heteroaggregation and the effect of aggregation on virus viability. Turbidity was measured on combinations of virus and each sediment type at low concentration to determine aggregation rates. Aggregation of sediment with virus occurred regardless of mineral type, and larger fraction of virus is expected to aggregate with increasing sediment concentration leading to higher deposition rates. The negatively charged sediments, aggregated with φ6 (also negatively charged at neutral pH) at a faster rate than the positively charged sediments, yielding turbidity slopes of 4.94 × 10-3 s-1 and 7.50 × 10-4 s-1 for φ6-montmorillonite and φ6-illite aggregates, respectively, and 2.98 × 10-5 s-1 and 2.84 × 10-5 s-1, for φ6-goethite and φ6-kaolinite, respectively. This indicates that the interaction between sediments and virus is hydrophobic, rather than electrostatic. Large numbers of virions remained viable post-aggregation, despite the fragility of the viral envelope, indicating that small-sized aggregates, which may travel more readily through porous media, may pose an infection risk. The fraction of φ6 that remained viable varied with sediment type, with montmorillonite-φ6 aggregates experiencing the greatest reduction in infectivity at 35%. TEM analyses reveal that in all sediment-φ6 combinations, infectivity loss was likely due to disassembly of the viral envelope as a result of aggregation.