The Saccharomyces cerevisiae viruses are non-infectious double-stranded (ds) RNA viruses present in most laboratory strains of yeast. Their genome consists of one or more dsRNAs separately encapsidated in particles composed mainly of one polypeptide, which has a Mr of 88 kdaltons in the best-studied viral subtype. A large viral dsRNA (L1, of 4.7 kb) encodes the capsid polypeptide. We have determined the sequences of a number of cDNA clones homologous to portions of L1 and mapped them by a novel heteroduplex technique. Several of these clones originate from a region of L1 2.3 - 2.5 kb from the 5′ end of the plus strand that contains stop codons in all three reading frames in the plus strand. We therefore suspect that the capsid polypeptide gene lies in the 5′ 2.3 - 2.6 kb of the plus strand. One of the cloned cDNAs has an inverted repeat of 17 bp that appears to be present in its parental RNA. The inverted repeat in L1 is the longest known inverted repeat in a viral dsRNA and the only known non-terminal inverted repeat. It might serve the function of creating two mRNAs from one viral dsRNA.
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