Different properties and functions have been assigned to tegument proteins such as proteins kinases, interferon inhibitors, apoptosis and host translation regulators. DTT removed lateral body proteins Chloramphenicol and uncovered proteins of the internal core wall. Cores treated with proteases could be disrupted and the internal components were uncovered. Cts8, a mutant in the A3 protein, produces aberrant virus that, when treated with NP-40 and DTT, release to the exterior the virus DNA associated with other internal core proteins. With these results, we are able to propose a model for the structure the vaccinia virion. == Introduction == Poxviridaecomprise a family of viruses characterized by the presence of a large dsDNA genome and a complex morphology (Condit et al., 2006;Moss, 2013). Poxviruses encode a complete transcription apparatus and Chloramphenicol thus are able to replicate in the cytoplasm of infected cells. Vaccinia virus (VACV), the prototype member of this family, encodes more than 200 proteins and the role of many virus proteins during the virus replicative cycle has been decided (Goebel et al., 1990;Moss, 2013). The protein composition of purified mature virions has been determined by mass spectrometry and at least 70 virus proteins have been identified (Chung et al., 2006;Matson et al., 2014;Resch et al., 2007;Yoder et al., 2006). Although the proteomic analysis has been important for the identification of the total protein content of the mature particle, the fine localization of a significant fraction of the virion proteins is still unknown. Membrane proteins and enzymes involved in early transcription have been assigned positions in the particle, but the location of the other proteins still needs to be decided. Electron microscopy is the preferred method for studying the morphology of the VACV particle and various electron microscopic techniques have been applied in the visualization of the HSF virus structure (Cyrklaff et al., 2005;Dales and Siminovith, 1961;Easterbrook, 1966;Harris and Westwood, 1964;Ichihashi et al., 1984;Muller and Peters, 1963;Naginton and Horne, 1962;Peters and Muller, 1963;Westwood et Chloramphenicol al., 1964;Wilton et al., 1995). Overall, poxvirus virions have an ellipsoidal, barrel or brick shaped appearance. Analysis of VACV on a whole mount preparation using unfavorable staining of the particles revealed the presence of a membrane that enclosed two distinct virus sub-domains: the lateral bodies and the core (Dales, 1962;Harris and Westwood, 1964;Muller and Peters, 1963;Peters and Muller, 1963;Westwood et al., 1964). The lateral bodies, which flank the core, are amorphous structures composed of proteins of unknown function. The core is comprised of a proteinaceous wall that encloses a nucleocapsid (Condit et al., 2006). Analysis of VACV by cryo-microscopy and reconstruction using electron tomography revealed pore-like structures spanning the core wall (Cyrklaff et al., 2005). No function has been determined for this structure although it could be involved in the extrusion from the core of the viral mRNA during early transcription. Using unfavorable staining electron microscopy, the surface of the mature virion presents two different morphological forms that Chloramphenicol are directly related to the integrity of the particle. The predominant form in a fresh virion preparation contains on its surface rodlet-like structures called surface tubule elements, creating a mulberry-like appearance (Harris and Westwood, 1964;Muller and Peters, 1963;Naginton and Horne, 1962;Westwood et al., 1964;Wilton et al., 1995). Under various conditions, the unfavorable stain can penetrate through the virus membrane so that the surface tubule elements are no longer apparent and the virus now exhibits a capsule-like form. When virions are exposed to high pH, the lateral bodies, core wall, and the nucleocapsid can be visualized (Muller and Peters, 1963). Analysis of VACV by atomic force microscopy has permitted a more.