ScV is a simple ds RNA virus with two, separately encapsidated dsRNAs. Like other fungal viruses, ScV particles are communicated from cell to cell only by mating. The larger viral dsRNA (L) encodes the major capsid protein. The smaller (M) encodes a toxin lethal to strains without ScV-M particles. INternal deletions of M result in defective-interfering (DI) particles containing fragments of M (ScV-S particles). Viral particles have a transcriptase activity. There are many unresolved questions about the ScV system that we hope to address in this project. A completed sequence analysis of L and M, combined with immunological screening for peptides predicted by sequence analysis should complete the catalog of viral proteins. An exact mapping of the in vivo and in vitro viral mRNAs will complement this analysis. There is no definitive evidence on the mechanism of transcription and replication of the viral dsRNAs. With the appropriate use of cDNAs cloned in the single-stranded phage M13, it should be possible to distinguish between conservative and semiconservative transcription in vitro. Suppression remains a useful phenomenon for understanding both viral interactions and virus-host interactions, since DI particles displace their parental virus by competing for some product present in limiting amount. The DI RNAs themselves will provide useful information about the viral transcriptase: a comparison of S dsRNAs should help us deduce signals for transcription termination and initiation. Combined with a complete analysis of the coding regions of M and similar sequence analysis of L, this comparison of S dsRNAs should define sites necessary for transcription initiation, replication, and packaging. Exact definition of such sites may become possible by construction of cDNA clones capable of expressing the complete viral plus strand in transformed yeast cells without indiginous virus, thus resurrecting the virus.
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