Self-cleavage of plus and minus RNA transcripts of avocado sunblotch viroid

Self-cleavage of both plus and minus RNA transcripts of the 247-residue avocado sunblotch viroid (ASBV), prepared from tandem dimeric cDNA clones, occurs specifically at two sites in each transcript to give monomeric plus and minus species. The cleavage reaction occurs both during transcription and on incubation of purified transcripts at pH 8 and 37 degrees C in the presence of magnesium ions to give a 3'-terminal 2',3'-cyclic phosphate and a 5'-terminal hydroxyl group. Although the self-cleavage occurs at different sites in the ASBV molecule for the plus and minus species, very similar secondary structures with high sequence homology can be drawn at each site. The results are considered to provide further evidence that ASBV is replicated in vivo by a rolling circle mechanism involving non-enzymic cleavage of high molecular weight RNA precursors of ASBV.