Non-enzymatic cleavage and ligation of RNAs complementary to a plant virus satellite RNA

Abstract

Small satellite RNAs1–5 of plant viruses depend on the presence of a supporting RNA virus for their propagation in vivo. Replication of the 359–nucleotide-long6 satellite RNA of tobacco ringspot virus (STobRV RNA) is detected only in tissue infected with tobacco ringspot virus (TobRV). STobRV RNA becomes encapsidated in TobRV coat protein and acts as a parasite of TobRV, reducing its accumulation and the severity of symptoms that it induces. Here we report the transcription in vitro of a circularly permuted, complementary DNA clone of STobRV RNA oriented so as to produce RNA that is complementary to the encapsidated, (+) polarity STobRV RNA. Like STobRV (+)RNA7, this dimeric, circularly permuted STobRV (−)RNA cleaves autolytically. Cleavage is at two identical sites generating monomeric-length RNA and two terminal fragments. The new termini are 5′-hydroxyl and 2′:3′-cyclic phosphodiester groups. The RNAs ligate spontaneously to give linear and, from the monomers, circular molecules. Replication of STobRV RNA may require these autoly-sis and ligation reactions, which, at least in vitro, occur without enzyme catalysis.