Interaction of replicase components between Cucumber mosaic virus and Peanut stunt virus

Cucumber mosaic virus (CMV) and Peanut stunt virus (PSV) each have genomes consisting of three single-stranded RNA molecules: RNA 1, 2 and 3. RNAs 1 and 2 encode the 1a and 2a proteins, respectively, which are necessary for replication of the viral genome. Although RNA 3 is exchangeable between CMV and PSV, exchange of RNA 1 and 2 between the two viruses has been unsuccessful. In this study, reassortants containing PSV RNA 1 and CMV RNA 2 together with RNA 3 of CMV or PSV were shown to be able to replicate their genomic RNA, but not to transcribe subgenomic RNA 4 in tobacco protoplasts. Conversely, the reassortant consisting of CMV RNA 1 and PSV RNA 2 together with RNA 3 of CMV or PSV could not replicate. Subsequently, a yeast two-hybrid system was used to analyse the in vivo interaction between the 1a and 2a proteins. The C-terminal half of PSV-1a protein interacted with the N-terminal region of 2a protein of both PSV and CMV, but the C-terminal half of CMV-1a and the N-terminal region of PSV-2a did not interact. These results suggest that RNA replication in the interspecific reassortant between CMV and PSV requires compatibility between the C-terminal half of the 1a protein and the N-terminal region of the 2a protein, and this compatibility is insufficient for transcription of subgenomic RNA 4.