Replication of satellite RNA in vitro by homologous and heterologous cucumoviral RNA-dependent RNA polymerases.

The RNA-dependent RNA polymerases (RdRp) of cucumber mosaic virus (CMV) and peanut stunt virus (PSV), members of the cucumovirus group, have been purified from virus infected plants and were used to study RNA synthesis in vitro using different viral RNAs, two cucumoviral satellites, and chimeric satellite cDNA clone transcripts as templates. The results show that solubilized RdRp preparations of CMV and PSV have a high degree of template dependency and catalyze (-) strand synthesis of the homologous cucumoviral RNAs with greater efficiency than the RNAs of heterologous cucumoviruses, although the PSV RdRp exhibits a lesser specificity than the CMV RdRp. On the other hand, both (-) and (+) strands of the satellite RNAs of CMV and PSV are synthesized by their homologous but not by the heterologous viral RdRps, indicating that recognition of satellites by the viral RdRp determines their replicative dependence upon specific helper viruses. Cucumoviral RdRp reactions using chimeric satellite transcripts suggest that the promoter structure for the satellite (-) strand synthesis resides in regions harboring the 3' termini of the two satellites.