INFECTIVITY OF LINEAR MONOMERIC TRANSCRIPTS OF CITRUS EXOCORTIS VIROID - TERMINAL SEQUENCE REQUIREMENTS FOR PROCESSING

Infectivity of linear monomeric viroid RNA transcripts is known to be dependent on the site of cloning of the viroid and the viroid and vect or sequences at the termini of the RNA transcripts. We report here the further characterization of cloning site and sequence requirements us ing 11 different monomeric cDNA constructs of citrus exocortis viroid; these differed from one another by the site of cloning and by nonviro id residues adjacent to the 5' and 3' termini of the viroid sequence i n the RNA transcript. The infectivity of these transcripts was assayed by inoculation onto tomato seedlings; all infectious transcripts were wild type, indicating accurate processing. The basic requirement for infectivity appeared to be the ability of the RNA transcripts to form a short double-stranded region of viroid and vector sequences at the j unction of the two termini. The site of cloning of the viroid RNA used for cloning was not important as cDNA clones prepared at seven sites provided infectious transcripts. (C) 1994 Academic Press, Inc.