Ultrastructure of the crystalline inclusion induced by tobacco etch virus visualized by freeze-etching

Structural subunits of the crystalline inclusion induced by tobacco etch virus were clearly resolved when inclusions were examined both in situ and in isolated preparations by freeze-etch electron microscopy. Data supported the contention that the crystal substructure is organized into laminae and that these laminae assemble into crystals by stacking vertically. The substructure of the laminae, revealed by examining isolated inclusions, appeared to consist of a single layer of subunits packed in rectangular array. When inclusions were cross-fractured in situ, subunits were evident in rectangular and semihexagonal arrays. Based on these observations a model is proposed for the arrangement of subunits in the crystal.