[Ultrastructural study of the effect of arginine deprivation on the morphogenesis of vaccinia virus]

Deep-etch EM reveals that the early poxvirus envelope is a single membrane bilayer stabilized by a geodetic "honeycomb" surface coat

Three-dimensional "deep-etch" electron microscopy (DEEM) resolves a longstanding controversy concerning poxvirus morphogenesis. By avoiding fixative-induced membrane distortions that confounded earlier studies, DEEM shows that the primary poxvirus envelope is a single membrane bilayer coated on its external surface by a continuous honeycomb lattice. Freeze fracture of quick-frozen poxvirus-infected cells further shows that there is only one fracture plane through this primary envelope, confirming that it consists of a single lipid bilayer. DEEM also illustrates that the honeycomb coating on this envelope is completely replaced by a different paracrystalline coat as the poxvirus matures. Correlative thin section images of infected cells freeze substituted after quick-freezing, plus DEEM imaging of Tokuyasu-type cryo-thin sections of infected cells (a new application introduced here) all indicate that the honeycomb network on immature poxvirus virions is sufficiently continuous and organized, and tightly associated with the envelope throughout development, to explain how its single lipid bilayer could remain stable in the cytoplasm even before it closes into a complete sphere.

A study of the ultrastructure of the buffalo pox virus

Buffalo pox virus (strain BP 4) has been studied by electron microscopy of sections of infected chorioallantoic membrane cells. The ultrastructure of the virus has been described and compared with the ultrastructure of vaccinia virus. No differences between the two viruses were found. In relation to the ways of release two forms of mature virions have been described. These are probably analogous to the previously described C- and M-form of vaccinia.