Multicomponent viruses fall into two groups on the basis of their sedimentation behavior. Some of them sediment as clearly defined two or multiple centrifugal components since the particles of each component have different shapes or sizes. Bromoviruses and cucumoviruses belong to the category of multicomponent viruses sedimenting as one nucleoprotein component. Capsid of long rods is composed of 1830 protein subunits and that of short rods of Dutch isolate is composed of 660 protein subunits. Capsid is composed of two different structural proteins present in equimolar amounts, a large protein of 44 kdaltons and a smaller protein of 25 kdaltons. Capsid is composed of 180 protein subunits arranged in 32 capsomeres. Cucumber mosaic virus is stabilized by protein-RNA interactions as suggested by the absence of empty protein capsids in vivo and in vitro. Primary stabilizing bonds occur between the positively charged basic residues of capsid polypeptide and negatively charged phosphate groups of RNA.