Comparative sequence studies of variants of avocado sunblotch viroid

The nucleotide sequences of 16 variants of the 247 nucleotide avocado sunblotch viroid (ASBV), purified from leaves of three avocado trees in separate locations, have been determined and compared with that of the previously published ASBV SB-1 sequence (Symons, R. H., Nucl. Acids Res. 9, 6527-6537, 1981). Most of the nucleotide differences were found to occur in the left- and right-hand loops of the ASBV molecule. The number of residues in the sequence variants varied from 246 to 251. Two sequence variants contained nucleotide changes in the double hammerhead-like self-cleaving structure identified in ASBV RNA. RNA transcripts of dimeric cDNA clones of these sequence variants retained their in vitro self-cleavage activity.