Three-dimensional reconstruction of the stacked-disk aggregate of tobacco mosaic virus protein from electron micrographs.

The three-dimensional structure of the stacked-disk rod of tobacco mosaic virus protein has been recon­ structed to a resolution of about 2 nm from electron microscope images. Closed rings of seventeen protein subunits (compared with 16^ in one turn of the virus helix) are stacked in polar fashion, the stacking being accompanied by an axial perturbation of periodicity 5.3 nm connecting successive pairs of rings into disks. The axial perturbation consists of a movement towards each other of the outer parts of the subunits in the two rings comprising a disk, together with a movement of the inner parts in the opposite direction. This could be explained either by a bending of parts of the subunits in the appropriate direc­ tions or by a bodily tilting of the subunits in the two rings in opposite directions.