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Conservative Transcription of Helminthosporium victoriae 190S Virus Double-stranded RNA in vitro

Department of Plant Pathology, University of Kentucky, Lexington, Kentucky 40546, U.S.A.

In in vitro reactions, the Helminthosporium victoriae 190S virus-associated RNA polymerase catalysed the synthesis and release of full-length ssRNA transcripts of genomic dsRNA. The transcriptase activity, which was dependent on virus concentration, required all four nucleoside triphosphates and magnesium ions. In reaction mixtures containing [³H]UTP, 99.0% to 99.5% of the incorporated label was in ssRNA. Hybridization analysis and in vitro translation of the reaction products showed that transcription was asymmetric and that the product of transcription was the message strand. In rabbit reticulocyte lysates, the in vitro transcript directed the synthesis of the capsid polypeptide p88. In transcription reactions containing [³H]UTP, no incorporated label was detected in genomic dsRNA during the time it took for the ssRNA transcript to reach full length. These results support the idea that transcription of dsRNA of this virus, like that of dsRNA of other members of the family Totiviridae, is conservative.

Keywords: Helmithosporium victoriae, transcription, conservative

Received 14 October 1988; accepted 26 January 1989.