Figure 1 Negatively stained preparations of a: (upper left) orthopoxvirus virion; (upper center) parapoxvirus virion and (upper right) yatapoxvirus virion. Virions of orthopoxviruses and yatapoxviruses are morphologically similar. Yatapoxviruses are always enveloped, whereas envelopment of orthopoxviruses is relatively rare. Parapoxvirus virions are smaller and are characterized by regular surface structures. The schematic structure of the orthopoxvirus virions (bottom left) reveals a condensed nucleoprotein organization of DNA. The core assumes a dumb-bell shape invaginated by the large lateral bodies, which are, in turn, enclosed within a protein shell about 12 nm thick - the outer membrane (or envelope), the surface of which appears to consist of irregularly arranged surface tubules, which in turn consist of small globular subunits. Some evidence suggests that the dumb-bell shape of cores may be an artifact of sample preparation. Virions released from the cell by exocytosis are enclosed within an envelope, which contains host cell lipids and several additional virus-specific polypeptides not present within intracellular virus. (E) The schematic structure of a parapoxvirus virus (Orf virus, ORFV) (bottom right) reveals an outer membrane consisting of a single, long tubule that appears to be wound around the particle. The bar represents 100 nm. (Redrawn from Fenner (1996) with permission.)
Figure 2 Schematic representation of the DNA of Vaccinia virus (VACV) (WR strain): (Top) Linear double-stranded molecule with terminal hairpins and inverted repeats (not to scale). The denatured DNA forms a single-stranded circular molecule. (Bottom) Hind III cleavage sites of the Vaccinia virus (WR strain) genome, the asterisk indicates the fragment that contains the thymidine kinase gene used in construction of phylogenetic trees. Each 10-kbp terminal portion includes two groups of tandem repeats of short sequences rich in AT. (Redrawn from Fenner, Wittek, and Dumbell, 1989, with permission.)
Figure 3 The infectious cycle of Vaccinia virus (VACV): IMV, intracellular mature virus; EEV, extracellular enveloped virus; VITF, vaccinia intermediate transcription factor; VLTF, vaccinia late transcription factor; VETF, vaccinia early transcription factor.
Figure 4 Phylogenetic relationship of poxviruses based on DNA polymerase (A), NTPase I (B), DNA Uracyl glycosylase (C) and thymidine kinase (D) gene sequences. Uprooted trees were constructed by maximum likelihood analysis with alignments of the complete proteins (PUZZLE v4.0; Strimmer, K. and A. von Haeseler, (1997). PNAS (USA) 94, 6815-6819). The scale represents a genetic distance of 0.1 as estimated by the Tamura-Nei model. Trees were drawn using TreeView (R.D.M. Page, (1996). CABIOS 12, 357-358).
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