THE TERMINI OF A NEW CITRUS VIROID CONTAIN DUPLICATIONS OF THE CENTRAL CONSERVED REGIONS FROM 2 VIROID GROUPS

A citrus viroid associated with dwarfing, CVdIIIA, has been sequenced and its 294 nucleotide residues can be arranged to form the typical ro d-like secondary structure of other viroids with 71% of nucleotides ba se-paired. CVdIIIA has greatest sequence similarity with apple scar sk in viroid (ASSVd; 69%) and has the central sequence which is conserved in the ASSVd group. CVdIIIA is the smallest member of the ASSVd group but contains the terminal conserved region shared by all viroids over 300 nucleotides. The two ends of CVdIIIA are highly unusual in that e ach end appears to be derived from the conserved central core region o f a different viroid group.