RNA recombination has been studied extensively in the plant virus genus Cucumovirus. Those studies have involved two of the three recognized viral species in this genus, Cucumber mosaic virus (CMV) and Tomato aspermy virus (TAV). These viruses both contain a single-stranded and positive-sense RNA genome divided into three species designated RNAs 1, 2 and 3 (14, 15) . RNA 1 encodes the 1a protein involved in virus replication (16, 17) . RNA 2 encodes two proteins: the 2a, also involved in virus replication (16, 17) and the 2b protein, involved in virus movement and the suppression of RNA silencing (18) (19) (20) (21) . RNA 3 also encodes two proteins, the 3a movement protein and the capsid protein, both of which are also involved in virus movement (22) (23) (24) . Protein 2b is translated from a subgenomic RNA of RNA 2, RNA 4A (25, 26) , while the capsid protein is translated from a subgenomic RNA of RNA 3, RNA 4 (27) . The 3 0 terminal 305-310-nt non-translated region (NTR) is nearly identical in each of the three genomic RNAs of each virus and represents promoters for (À) viral RNA synthesis during viral replication (23, 28, 29) . The location of most of the recombinants described involving CMV and TAV is within these 3 0 NTR sequences.