Crystalline aggregates observed in the vicinity of freeze-etched poxvirus inclusions

Freeze-etching has revealed the presence of crystalline aggregates closely associated with the developing viral inclusion of vaccinia virus. These have not been observed in frozen uninfected cells or, as yet, in infected cells processed by chemical fixation. Two types apparently exist, linear aggregates composed of cubically packed units, about 10 nm in size, and curved sheets or lamellae in which the subunits, each about 7.5 nm in size, are arranged hexagonally. The precise nature of these aggregates is undetermined, although the latter type is thought by analogy with other poxvirus systems to be related to the surface component of immature virions.