Abstract
Particles of tobacco ringspot nepovirus from purified preparations were trapped on grids by immunosorbent electron microscopy and then either negatively stained, or freeze-dried and shadowed with uranium, for structural studies. Particle dimensions differed considerably with different stains and methods of preparation, but no obvious substructure was apparent. In contrast, particles which were freeze-dried and then shadowed exhibited either fivefold or threefold symmetry and had a structure resembling that of models made up of 60 units in clusters of five arranged in a T = 1 lattice. Both chemical and morphological evidence are compatible with this structure.