P. J. G. Butler and A. Klug, "The Assembly of a Virus," Scientific American, 1978

STAGES IN THE SELF-ASSEMBLY OF TOBACCO MOSAIC VIRUS

(a) Intercalation of the initiation region of RNA into a disk of capsid monomers. (b) Binding of RNA and dislocation of the disk into a "lock washer." (c) A second disk adds on top of the first. (d) Elongation of the virion.