- Volume 93, Issue 3, 2012

We report the identification of a novel single-stranded, circular DNA virus isolated from bovine stool. The virus, named bovine stool-associated circular DNA virus (BoSCV), has a genome comprising 2600 bases of circular ssDNA, with two putative ORFs encoding replicase and capsid proteins, arranged inversely. The stem–loop structure was located between the 3′ ends of the two putative ORFs, as in chimpanzee stool-associated circular virus (ChimpSCV) and unlike other circular DNA viruses, including members of the families Circoviridae, Nanoviridae and Geminiviridae. BoSCV was also genetically similar to ChimpSCV, with approximately 30 % identity in the replicase and capsid proteins. A phylogenetic analysis based on the replicase protein showed that BoSCV and ChimpSCV are in the same clade. A field survey using BoSCV-specific PCRs targeting ORF1 detected BoSCV and BoSCV-like sequences in bovine and porcine stool samples. BoSCV appears to belong to a new genus of circular DNA viruses.

Inoculation of the semi-persistent cauliflower mosaic virus (CaMV, genus Caulimovirus) is associated with successive brief (5–10 s) intracellular stylet punctures (pd) when aphids probe in epidermal and mesophyll cells. In contrast to non-persistent viruses, there is no evidence for which of the pd subphases (II-1, II-2 and II-3) is involved in the inoculation of CaMV. Experiments were conducted using the electrical penetration graph (EPG) technique to investigate which particular subphases of the pd are associated with the inoculation of CaMV to turnip by its aphid vector Brevicoryne brassicae. In addition, the same aphid species/test plant combination was used to compare the role of the pd subphases in the inoculation of the non-persistent turnip mosaic virus (TuMV, genus Potyvirus). Inoculation of TuMV was found to be related to subphase II-1, confirming earlier results, but CaMV inoculation appeared to be related exclusively to subphase II-2 instead. The mechanism of CaMV inoculation and the possible nature of subphase II-2 are discussed in the scope of our findings.

Generation of an abnormal isoform of the prion protein (PrPSc) is a key aspect of the propagation of prions. Elucidation of the intracellular localization of PrPSc in prion-infected cells facilitates the understanding of the cellular mechanism of prion propagation. However, technical improvement in PrPSc-specific detection is required for precise analysis. Here, we show that the mAb 132, which recognizes the region adjacent to the most amyloidogenic region of PrP, is useful for PrPSc-specific detection by immunofluorescence assay in cells pre-treated with guanidine thiocyanate. Extensive analysis of the intracellular localization of PrPSc in prion-infected cells using mAb 132 revealed the presence of PrPSc throughout endocytic compartments. In particular, some of the granular PrPSc signals that were clustered at peri-nuclear regions appeared to be localized in an endocytic recycling compartment through which exogenously loaded transferrin, shiga and cholera toxin B subunits were transported. The granular PrPSc signals at peri-nuclear regions were dispersed to the peripheral regions including the plasma membrane during incubation at 20 °C, at which temperature transport from the plasma membrane to peri-nuclear regions was impaired. Conversely, dispersed PrPSc signals appeared to return to peri-nuclear regions within 30 min during subsequent incubation at 37 °C, following which PrPSc at peri-nuclear regions appeared to redisperse again to peripheral regions over the next 30 min incubation. These results suggest that PrPSc is dynamically transported along with the membrane trafficking machinery of cells and that at least some PrPSc circulates between peri-nuclear and peripheral regions including the plasma membrane via an endocytic recycling pathway.