Figure 1 Betatetravirus capsid structure. (Left) Schematic representation of a T=4 icosahedral lattice. (Center and Right) Cryo-electron microscopy image reconstruction of a particle of Nudaurelia capensis β virus (NβV) on the symmetry axis 3 and 5; the bar represents 20 nm.
(Courtesy of H.R. Cheng, N. Olson and T. Baker.)
Figure 2 Tetravirus genome comparisons. The genome organization, including genome segments, ORFs and selected domains, is depicted for four tetraviruses, EeV, NβV, HaSV and PrV, using virus-specific scales. EeV, NβV and PrV have monopartite genomes that (are predicted to) yield sgRNAs, while HaSV has a bipartite genome (RNA1 and RNA2). The selected proteins and domains are labelled, pattern-coded and coloured to indicate homology. nmT: N7-methyltransferase; HEL1, superfamily 1 helicase; acRdRp: canonical RNA dependent RNA polymerase typical of alpha-like supergroup; ccRdRp: canonical RNA dependent RNA polymerase typical of carmo-like supergroup; pRdRp: non-canonical permuted RNA-dependent RNA polymerase most related to picorna-like supergroup; NPGP: 2A-like processing site. The sequence of the major (L or β) and minor (S or γ) capsid proteins are indicated as “L” and “S”, respectively.
(Modified from Figure 1 of Zeddam et al. (2010). Virology, 397, 145-154.)
Figure 3 Comparison of tetravirus capsid morphologies. Cryo-electron microscopy reconstructions of capsids of the omegatetraviruses, Nudaurelia capensis ω virus (NωV) and Helicoverpa armigera stunt virus (HaSV) and the betatetraviruses, NβV and PrV. The structures, viewed down their two-fold axes, were determined at resolutions of between 25 and 30 Å.
(Image taken from Figure 2 of Speir and Johnson (2008); with permission.)
Figure 4 Phylogeny of tetravirus capsid protein. The tree for seven tetraviruses is based on an amino acid alignment of the jelly-roll domain of L protein (661 positions) and was rooted using the jelly-roll domain of S proteins of five birnaviruses as an outgroup. Numbers at branch points provide Bayesian posterior probability support values and the evolutionary scale is indicated by the bar of 0.5 amino acid substitutions per site on average.
(Modified from Figure 5b (left part) of Zeddam et al. (2010). Virology, 397, 145–154.)
Figure 5 Phylogeny of prototypic tetravirus replicases. The tree for prototypic tetraviruses and DpTV is based on an amino acid alignment of the HEL1 and acRdRp domains (832 positions) and was rooted using avian and human Hepatitis E viruses as an outgroup. Numbers at branch points provide Bayesian posterior probability support values and the evolutionary scale is indicated by the bar of 0.5 amino acid substitutions per site on average.
(From Figure 5b (right part) of Zeddam et al. (2010). Virology, 397, 145–154.)
Figure 6 Unrooted phenogram showing the relationships of the RdRps of the tetraviruses TaV and EeV to other virus families and viruses in the “picornavirus-like supercluster”. The pRdRps of TaV, EeV and the birnaviruses were converted into the canonical form by relocating the motif C sequence (18–20 aa) downstream of the motif B, as in canonical polymerase motifs. These sequences were aligned with those of polymerases from representative viruses in the Picornaviridae, Dicistroviridae, Secoviridae, Iflaviridae, Caliciviridae, Potyviridae, Coronavirinae, Torovirinae, Roniviridae, Arteriviridae and unclassified insect viruses. Using an extended, gap-free version of the alignment containing 332 informative characters, an unrooted neighbor-joining tree was inferred by the ClustalX1.81 program. All bifurcations with support in>700 out of 1000 bootstraps are indicated. Different groups of viruses are highlighted. Virus families and groups, viruses included in the analysis, abbreviations ( ) and the NCBI protein (unless otherwise specified) IDs [ ] are as follows: Picornaviridae: human poliovirus type 3 Leon strain (PV-3L)  and human parechovirus 1 (HpeV-1) ; Iflaviridae: infectious flacherie virus (InFV) ; unclassified insect virus Acyrthosiphon pisum virus (APV) ; Dicistroviridae: Drosophila C virus (DCV) ; Secoviridae: rice tungro spherical virus (RTSV) , parsnip yellow fleck virus (PYFV) , cowpea severe mosaic virus (CPSMV)  and tobacco ringspot virus (TobRV) ; Caliciviridae: feline calicivirus F9 (FCV-F9)  and Lordsdale virus (LORDV) ; Potyviridae: tobacco vein mottling virus (TVMV)  and barley mild mosaic virus (BaMMV) ; Coronavirinae: human coronavirus 229E (HCoV) ; Torovirinae: Berne torovirus (BEV) ; Arteriviridae: equine arteritis virus (EAV) ; Roniviridae: gill-associated virus (GAV) ; Tetraviridae: Thosea asigna virus (TaV) [AF82930; nt sequence] and Euprosterna elaeasa virus (EeV) [AF461742; nt sequence]; Birnaviridae: infectious pancreatic necrosis virus (IPNV)  and infectious bursal disease virus (IBDV) . Coronaviridae, Arteriviridae and Roniviridae belong to the order Nidovirales.
(Modified from Gorbalenya et al., 2002.)
Figure 7 Phylogeny of Providence virus (PrV) and related tombus- and umbravirus RdRps. The tree is based on an amino acid alignment of the C-terminal half of the replicase starting after the read-through stop codon (578 positions) encoding putative RdRp and was midpoint pseudo-rooted. Poorly conserved alignment termini were discarded from the analysis. Tombus- and umbraviruses encode RdRps that are the closest to the PrV RdRp as determined in a protein Blast analysis. The RdRp tree was calculated and depicted following procedures and a style adopted by Zeddam et al. (2010) (see Figures 4 and 5). The relaxed lognormal molecular clock model allowing different branches of the tree to “evolve” at different rates was used. Numbers at branch points provide Bayesian posterior probability support values and the evolutionary scale is indicated by the bar of 0.1 amino acid substitutions per site on average. RefSeq accession numbers are indicated next to the virus names. This tree is by Lauber and Gorbalenya (unpublished) using the PrV sequence (GenBank accession no: AF548354).