The current picture of the structure and assembly of tobacco mosaic virus.

Introduction. Tobacco mosaic virus (TMV) has long been a favourite object for studies on both the structure and assembly of rod-shaped viruses. Soon after its initial purification by Stanley (1935) investigations of its structure were begun using both chemical and X-ray diffraction techniques (Bawden & Pirie, 1937; Bernal & Fankuchen, 1941). Moreover, the problems in solving such a large structure led to many developments in techniques. Since the virus has a helical structure (Watson, 1954) and forms an extremely well oriented gel rather than crystals, the three-dimensional structural information is convoluted into two dimensions because of the azimuthal disorder of the particles in the gel. Despite this difficulty, techniques have been evolved allowing the virus structure to be solved to a resolution approaching 0.4 nm (Stubbs et al., 1977). The protein alone will form true crystals as one of its aggregates (the disk; see below) the structure of which has been solved to a resolution of 0.3 nm (Champness et al., 1976; Bloomer et al., 1978), allowing a detailed atomic model to be built.