The tobacco mosaic virus particle: structure and

A short account is given of the physical and chemical studies that have led to an understanding of the structure of the tobacco mosaic virus particle and how it is assembled from its constituent coat protein and RNA. The assembly is a much more complex process than might have been expected from the simplicity of the helical design of the particle. The protein forms an obligatory intermediate (a cylindrical disk composed of two layers of protein units), which recognizes a speci¢c RNA hairpin sequence. This extraordinary mechanism simultaneously ful¢ls the physical requirement for nucleating the growth of the helical particle and the biological requirement for speci¢c recognition of the viral DNA