Five Virusoid RNA genomes are 220-338 nucleotides long, circular, single stranded and possess a ribozyme activity. They can replicate in the cytoplasm using an RNA-dependent RNA polymerase. This enzymatic activity is common in plants but not found in animal cells. They depend on a helper virus for replication. This helper virus also encapsidates them, e.g: Subterranean clover mottle virus satellite RNA: Helper - Sobemovirus