Biophysical and biochemical properties of wild cucumber mosaic virus and of two related virus-like particles

Plants infected with wild cucumber mosaic virus produce two virus-like particles (designated top component a and top component b) in addition to virus (designated bottom component). The bottom component and a mixture of top component a and top component b were isolated by means of sucrose-density gradient centrifugation. The molecular weights, determined by sedimentation and diffusion experiments, were 4.0·106 for top component a, 4.3·106 for top component b, and 7.0·106 for bottom component. These particles differ in their nucleic acid content. Top component a has no nucleic acid, top component b contains approx. 11% RNA, and bottom component contains approx. 35% RNA. The relative proportion of the 4 nucleotide bases in the RNA of top component b and in the RNA of bottom component are similar. Both have an unusually high proportion of cytosine. The amino acid compositions of the three components are quite similar.