Electron microscope observations on the structure of turnip yellow mosaic virus

Electron micrographs of turnip yellow mosaic virus particles prepared by the negative staining technique show clearly defined internal structure, which indicates that the protein shell of this virus is constructed of 32 subunits in an icosahedral arrangement. The structure inferred from the electron micrographs satisfies the X-ray data, and contains subunits which occupy two structurally distinct sites.