RNA-protein interactions in alfalfa mosaic virus.

Particles of the bottom component of alfalfa mosaic virus have a compact bacilliform structure at neutral pH. When the pH is raised to 8.3 the structure unfolds. Since the particle weight does not change it is concluded that the protein subunits remain attached to the RNA. The particle weight of the spheroidal top component a of the virus is halved when the particles unfold at pH 8.3. This can be explained by the fact that these particles contain two RNA molecules of identical size. Free RNA molecules of alfalfa mosaic virus are able to withdraw protein subunits from intact particles of the virus. It is demonstrated that per RNA molecule there are a few sites with a high affinity for coat protein. Possibly these are the sites where the coat protein plays its role in activating the genome.