Infectivity and in vitro mutagenesis of monomeric cDNA clones of citrus exocortis viroid indicates the site of processing of viroid precursors.

Abstract

Monomeric cDNA clones of citrus exocortis viroid (CEV) were constructed in the plasmid vector pSP6-4 and the infectivity of the clones plus in vitro-synthesized RNA transcripts determined by inoculation onto tomato seedlings. Infectivity was dependent on the site of the viroid molecule used for cloning and the orientation of the cDNA insert. Only the plus BamHI cDNA clone was infectious and produced progeny viroid with wild-type sequence at the region corresponding to the BamHI cloning site. Infectivity correlated with the terminal repetition of 11 nucleotides of viroid sequence, 5'GGATCCCCGGG 3', in the vector adjacent to the insert. The 11-nucleotide sequence lies within the highly conserv..