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

Abstract

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.

Parallel evolution of picobirnaviruses from distinct ancestral origins

“…We explored the secondary structure of the 5′UTR in bacteriophage phi6 and obtained the formation of several stem-loops resembling IRES-like structures which stabilize the SD region (Fig. S6C) and previously described as alterative translation strategy for this viral species (reviewed in reference 18 ). Experimental evidence in agreement with our findings is manifested in the inability of PBV to replicate in bacterial culture, although this one example is not conclusive of the lack of potential to do so, and future experiments may prove otherwise ( 8 ).…”

Discovery and Classification of the φ6 Bacteriophage: An Historical Review

“…The protein seemed to appear as a double in the cell lysate autoradiograms and single in the proteins isolated from the bacteriophage particles. Later structural studies would show that P8 had different conformations when assembled into the matrix layer, consisting two states of interdigitating P8 trimers that are designated as either open or closed, possibly accounting for the initial erroneous interpretation [ 31 ]). The physical effect of the addition of different concentrations of Triton X-100 were imaged by electron microscopy in phosphotungstic acid (PTA) negatively stained samples, showing progressive removal of the envelope and exposed nucleocapsid.…”

RNA and Single-Stranded DNA Phages: Unveiling the Promise from the Underexplored World of Viruses

“…All known dsRNA phages infect Gram-negative bacteria, mainly plant-pathogenic Pseudomonas syringae strains [35]. Until 1999, the Pseudomonas phage phi6 was the sole species of the Cystoviridae family [38]. Additional lipid-containing, three-segmented dsRNA phages were subsequently isolated into two groups: Those closely related (phi 7, phi9, phi10, and phi11) and those distantly related (phi8 and phi12) to phi6.…”

“…Phi6 and its closely related relatives utilize type IV pili as the host receptor, limiting their infection range to P. syringae and several mutants of P. pseudoalcaligenes ERA [39]. In contrast, phi8 and phi12 infect P. syringae with rough LPS [38]. Phi8, phi12, and phi13 could infect other rough-LPS-containing Gram-negative bacteria, though plaque formation was not observed when phi12 was used to infect JM109 [39].…”

“…With their segmented dsRNA genome, dsRNA phages share similarities with the family Reoviridae, a diverse family consisting of plant, fungi, invertebrate, and vertebrate viruses. Therefore, dsRNA phages provide opportunities to study the genome packaging and assembly mechanisms of dsRNA-segmented genome viruses in a simple and easy-to-handle prokaryotic system [38].…”