Assembly of rod-shaped virus in vitro: reconstitution with cucumber green mottle mosaic virus protein and tobacco mosaic virus RNA.

In vitro assembly of tobacco mosaic virus (TMV) from its constituent RNA and protein occurs in two steps: formation of the initial complex by interaction of the 5'-end of TMV-RNA with 20S protein aggregate, and growth of the helical rod by sequential addition of protein subunits.Such a process was also observed in the assembly of cucumber green mottle mosaic virus, which is also a rodshaped virus. The 13S virus-protein aggregate, probably a single-ring structure, is needed for formation of the initial complex, instead of the 20S double-ring structure for TMV. The 13S aggregate cannot effect growth of the initial complex to a long infective rod. Rod elongation takes place by the sequential addition of protein subunits. In general, the assembly of rod-shaped viruses occurs in two steps, and the protein aggregate is essential only for initiation of the reaction, not for rod elongation.