DEFECTIVE RNA MOLECULES ASSOCIATED WITH CITRUS TRISTEZA VIRUS

Preparations of single-stranded (ss) RNA extracted from particles of t he Israeli VT strain of citrus tristeza virus (CTV-VT), and ss- and do uble-stranded (ds) RNA preparations extracted from infected Alemow (Ci trus macrophylla) plants, contained a population of molecules with fea tures that suggest that they are defective RNAs. The prototype of 2424 nt was cloned and sequenced and was found to be composed of two genom ic regions corresponding to the 5' (1151 nt) and the 3' (1259 nt) term ini of the genomic CTV-RNA, with two perfect direct repeats of eight n ucleotides of unknown origin at the junction site. Northern hybridizat ion analysis demonstrated that this 2.4-kb defective RNA is an abundan t species among the other CTV-specific ss- and ds-RNAs in infected pla nts. The 2.4-kb RNA was found encapsidated by the CTV coat protein ind icating that the CTV origin of assembly is located close to the 5' or 3' terminus. This is the first defective RNA to be reported for a memb er of the closterovirus group. (C) 1995 Academic Press, Inc.