In vitro Transcription of Double-stranded RNA by Virion-associated RNA Polymerases of Viruses from Gaeumannomyces graminis

Several double-stranded (ds) RNA Gaeumannomyces graminis viruses in groups I and II, but none in group III, have been shown to possess virion-associated RNA polymerase activity. The products of polymerase reaction were full-length single-stranded (ss) RNA transcripts of one of the strands of each of the dsRNA genome segments. Synthesis of ssRNA in vitro continued for up to 48 h during which, on average, up to eight full-length transcripts were produced per dsRNA molecule, i.e. reinitiation of transcription occurred in the in vitro system. In reactions containing [3H]UTP, label was also incorporated into all the dsRNA genome segments, reaching a maximum after 8 h. Examination of transcribing particles by electron microscopy revealed the presence of particles showing the release of looped ssRNA molecules, both ends of which were attached to the particle, as well as particles with one or two linear RNA strands attached. The modal length of the single linear RNA strands was within the range expected for full-length transcripts of the genome dsRNA segments.