Subcellular localization of cucumovirus-associated satellite double-stranded RNAs

Viral satellites are small RNAs that depend on the presence of the specific helper virus for replication and that can modulate viral disease expression. The in vivo subcellular location of the double-stranded (ds) form of different Cucumovirus-associated satellite RNAs, which accumulate in large quantities in infected tobacco plants, is reported here. Subcellular fractions were obtained by differential centrifugation and characterized by their specific nucleic acid content and by electron microscopy. Results indicate that the viral and satellite ds-RNAs copurify with a size-homogeneous vesicular fraction. A similar vesicular fraction was also isolated from healthy tobacco plants. The results suggest that the replication of satellite RNAs occurs in close association with these vesicles and are consistent with the hypothesis of the satellite dependence on the viral-coded replicase.