Figure 1 Electron micrographs of negatively stained preparations of: (left) an orthopoxvirus mature virion; (center) a parapoxvirus mature virion and (right) a yatapoxvirus enveloped virion. The bar represents 100 nm.
(From Esposito, J.J. and Fenner, F. (2001). Poxviruses. In: Fields Virology, 4th edn (D.M. Knipe and P.M. Howley, Eds.), Lippincott Williams & Wilkins, Philadelphia, PA, pp. 2885-2921; with permission.)
Figure 2 Schematic representation of the genome of the WR strain of vaccinia virus (AY243312). The genome is a linear double stranded molecule with terminal hairpins, inverted terminal repeats (ITR) and a series of direct repeats within the ITRs. Coloured rectangles represent each WR gene and the arrow at one end of each rectangle indicates the direction of transcription for that gene from the DNA template. The VACWR name represents the GenBank locus name for each gene. The coloured overlapping gene rectangles indicate the extent to which each gene is conserved (present or absent) in all poxviruses, vertebrate poxviruses (chordopoxviruses) and orthopoviruses. The bars are colour-coded according to the percentage of gene conservation across the indicated taxa.
Figure 3 The infectious cycle of poxviruses, based primarily on that of vaccinia virus (VACV): ATI, A-type inclusion body; IV, immature virion; MV, mature virion; WV, wrapped virion; EV, enveloped virion; CEV, cell-associated enveloped virion. See text for full details. (1) Disruption of envelope of EV upon binding to cell surface receptors, essentially revealing MV, which like naked MV can (2) fuse directly with the cell membrane (mediated by the fusion complex) to release the naked core (and lateral bodies). The core is (3) transported to the perinuclear region along microtubules. Early genes are expressed (wavy arrows) directly from the intact core; early gene products mediate: (4) uncoating of the core, (5) DNA replication and intermediate gene expression. Intermediate gene products (with involvement of some host proteins derived from the nucleus) mediate late gene expression. Late gene products include structural proteins (including polymerase required for early gene expression) and proteins required for morphogenesis. Single membrane crescents are assembled (6) to enclose viral core proteins and genomic DNA (the latter is cleaved from concatameric intermediates), forming IV. These mature (7) to MV that, in VACV and many other mammalian poxviruses, are transported to the trans-Golgi/endosomal compartment for (8) wrapping with a double membrane to produce WV. These are (9) transported to the cell surface along microtubules, where they (10) exocytose, losing the outer of the two additional membranes, to form EV. The EV can remain on the cell surface as CEV or become free in the medium. CEV can (11) be propelled away from the cell on the tips of actin-driven projections. MV of some poxviruses can (12) alternatively be transported to and incorporated into ATI. The avipoxviruses do not appear to form WV to any significant extent, rather production of EV involves MV transport to the plasma membrane where they undergo budding to exit the cell (13).
Figure 4 Panel A: Phylogenetic relationships in the family Poxviridae. Phylogenetic predictions are based upon aligned amino acid sequences from 19 conserved genes of virus isolates from representative species of each genus. Genera are indicated by bold, italic text, while species are represented in italic text. Branches with dotted lines indicate virus isolates for which limited sequence information is available and therefore their placement on the tree is not definitive. The species Squirrel poxvirus has not yet been assigned to a genus. Unclassified viruses have not yet been assigned to a taxon. There are no sequenced isolates within the genus Gammaentomopoxvirus. Panel B: Phylogenetic relationships in the genus Orthopoxvirus. Phylogenetic predictions are based upon codon-aligned nucleic acid sequences from nine conserved genes of isolates from each species. Two strains of cowpox virus were included in the analysis to demonstrate the discordant placement of different isolates of this species on the genus tree. Tree topologies for both analyses were inferred using Bayesian analysis as implemented by the program MrBayes.