Preliminary analysis of crystals of satellite tobacco mosaic virus.

Satellite tobacco mosaic virus (STMV), a small T = 1 icosahedral plant virus, has been crystallized in a form suitable for high-resolution X-ray diffraction analysis. The crystals, which diffract to better than 2.5 A resolution, are of space group I222 and have unit cell dimensions of a = 176 A, b = 192 A and c = 205 A. The centers of the virus particles occupy 222 symmetry points in the unit cell and one quarter of the virus particle constitutes the asymmetric unit, which is therefore comprised of 15 capsid protein molecules. From packing considerations, the maximum diameter of the STMV particles cannot exceed 165 A, and it is probably 5 to 10 A less than this value.