Electron microscopic evidence on the structure of the particles of tobacco rattle virus

The structure of tobacco rattle virus was studied by examining with the electron microscope: (1) shadow-cast mounts of particles partly degraded with alkali, sodium dodecyl sulphate or phenol; (2) unshadowed mounts on thin carbon film of particles treated with solutions of lanthanum nitrate, uranyl acetate, osmium tetroxide, phosphomolybdic acid or phosphotungstic acid.

The particles were tubular, with a central hole of approximately 4 mμ diameter and an outside diameter which varied from 17 to 25 mμ according to treatment. Next to the central hole, which could be filled with lanthanum nitrate or with uranyl acetate, was a region 1–1·5 mμ thick, which stained heavily with osmium tetroxide, phosphomolybdic and phosphotungstic acids. The rest of the particle stained lightly with uranyl acetate, phosphomolybdic and phosphotungstic acids, and showed transverse bands 2·5 mμ apart. It is suggested that these bands may represent a helical structure similar to that of tobacco mosaic virus, which tobacco rattle virus resembles in many respects.