AbstractRaspberry bushy dwarf virus (RBDV; genus Idaeovirus) has a bipartite genome that consists of a ca. 5.4 kb RNA-1 and a ca. 2.2 kb RNA-2. RNA-1 encodes the proteins that are involved in virus replication. Near the 3′ end of the major open reading frame (ORF) of RNA-1, we have identified a second, overlapping but out-of-frame ORF that encodes a 12K protein. The position of this gene corresponds to that of the 2b gene in the genome of cucumber mosaic virus (CMV). The CMV 2b protein is not essential for infectivity, but it does play a role in long distance movement of CMV in infected plants and in the suppression of post-transcriptional gene silencing. Small ORFs have also been identified in similar positions in the genomes of a number of viruses in the family Bromoviridae. We have compared RNA-1 sequences of a number of RBDV isolates. All contained a small ORF in this 3′ region. However, the ORF was shorter in several of these RNAs, and the encoded polypeptides were correspondingly truncated at their C-termini.