RATTLESNAKE STRUCTURE OF A FILAMENTOUS PLANT RNA VIRUS BUILT OF 2 CAPSID PROTEINS

Elongated particles of simple RNA viruses of plants are composed of an RNA molecule coated with numerous identical capsid protein subunits t o form a regular helical structure, of which tobacco mosaic virus is t he archetype. Filamentous particles of the closterovirus beet yellows virus (BYV) reportedly contain approximate to 4000 identical 22-kDa (p it) capsid protein subunits. The BYV genome encodes a 24-kDa protein ( p24) that is structurally related to the p22. We searched for the p24 in BYV particles by using immunoelectron microscopy with specific anti bodies against the recombinant p24 protein and its N-terminal peptide, A 75-nm segment at one end of the 1370-nm filamentous viral particle was found to be consistently labeled with both types of antibodies, th us indicating that p24 is indeed the second capsid protein and that th e closterovirus particle, unlike those of other plant viruses with hel ical symmetry, has a ''rattlesnake'' rather than uniform structure.