Figure 1 (A) Fivefold averaged cryo-electron micrographs of Paramecium bursaria chlorella virus PBCV-1 reveal a long, thin, cylindrical spike structure at one vertex and protrusions (fibers) extending from one unique capsomer per trisymmetron (from Cherrier et al. (2009). Proc. Natl Acad. Sci., U S A, 106, 11085-89; with permission). (B) Putative tail structure (arrowed) can be observed in Emiliania huxleyi virus EhV-86 in the cytoplasm of infected Emiliania huxleyi before release of progeny virions (approx. 3 h p.i.) (adapted from Mackinder et al. (2010). J. Gen. Virol., 90, 2306-2316; with permission). (C) PBCV-1 attached to the cell wall of its host as viewed by the quick-freeze, deep-etch procedure. Note: fibers attach the virus to the wall (photo courtesy of John Heuser). (D) EhV-86 virion showing the putative internal lipid membrane (arrowed)
(photo courtesy of Willie Wilson).
Figure 2 (Top) Genome organization of PBCV1. (Bottom) Circular map of the EsV-1 genome. Inner circle, sites for restriction endonucleases AscI and SfiI. Outer circle, nucleotide, coordinates and position of repeat regions (block rectangles: B, C, C’, etc). Triangles, the inverted terminal repeats, ITRs A and A′.
Figure 3 Schematic of the proposed life cycle of EhV-86. Enveloped EhV-86 enters E. huxleyi with an intact capsid and nucleoprotein core either by an endocytotic mechanism (step 1a) followed by fusion of its envelope with the vacuole membrane (step 2) or by fusion of its envelope with the host plasma membrane (step 1b). The viral capsid encapsulated nucleoprotein core rapidly targets the nucleus where capsid breakdown releases the viral genome (step 3). The viral genome enters the host nucleus where early promoter sequences are expressed by host RNA polymerase. Mid-late genes are expressed by viral RNA polymerase within the cytoplasm where capsid assembly takes place, possibly by filling of a pro-capsid with viral DNA and core proteins (step 4). Early assembled viruses are transported to the plasma membrane (step 5) where they are released by a budding mechanism (step 6)
(from Mackinder et al. (2010). J. Gen. Virol., 90(9), 2306-2316; with permission).
Figure 4 Phylogenetic analysis of members of the family Phycodnaviridae based on a distance matrix algorithm between the amino acid sequences of DNA pol fragments of phycodnaviruses and other large dsDNA viruses (Neighbor in PHYLIP, version 3.61). The alignment was performed (ClustalW) on the region spanning the highly conserved regions I and IV of the DNA pol genes. Abbreviations: Micromonas pusilla virus (MpV); Ostreococcus tauri virus (OtV); paramecium bursaria chlorella virus (PBCV); Emiliania huxleyi virus (EhV); Ectocarpus siliculosus virus (EsV); Feldmannia irregularis virus (FirrV); Feldmannia species virus (FsV), Chrysochromulina ericina virus (CeV); Pyramimonas orientalis virus (PoV); Chysochromulina brevifilum virus (CbV); Phaeocystis globosa virus (PgV); Heterosigma akashiwo virus (HaV); equid herpesvirus (EHV); alcelaphine herpesvirus (AlHV); bovine herpesvirus (BOHV); African swine fever virus (ASFV); Autographa californica multiple nucleopolyhedrovirus (AcMNPV); Bombyx mori nucleopolyhedrovirus (BmNPV); Lymantria dispar multiple nucleopolyhedrovirus (dMNDV); Helicoverpa zea single nucleopolyhedrovirus (HzSNPV); Chironomus luridus entomopoxvirus; (CLEV); vaccinia virus (VACV); fowlpox virus (FWPV); molluscum contagiosum virus (MOCV); invertebrate iridescent virus (IIV; family Iridoviridae). The scale bar indicates a distance of 0.2 fixed mutations per amino acid.
(Courtesy of Ilana Gilg.)