| viroid | <plant biology, virology> Extremely small viruses of plants. Their genome is a 240-350 nucleotide circular RNA strand, extensively base paired with itself, so they resist RNAase attack. At one time the term was also used casually of self replicative particles such as the kappa particle in Paramecium. (13 Oct 1997) |
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| viroids | A group of pathogens comprising the smallest known agents of infectious disease. They are unencapsulated and are capable of replicating autonomously in susceptible cells. Positively identified viroids composed of single-stranded RNA have been isolated from higher plants, but the existence of DNA viroids pathogenic to animals is suspected. (12 Dec 1998) |