Structure and expression of the M₂ genomic segment of a type 2 killer virus of yeast

The M₂ double-stranded (da) RNA apeciea encodes toxin and resistance functions in Saccharomyces cereviaiae straina with the K₂ killer specificity. RNA sequence analysis reveals the presence of a large open reading frame on the larger heat-cleavage product of M₂ dsRNA, which is translated in vitro to yield a 28 kd polypeptide as a major product. The postulated translation initiator AUG triplet is located within a stem and loop structure near the 5′terminus of the positive strand, which also contains plausible 16S and 5.8S ribosomal RNA binding sites. These features nay serve to regulate the translation of the K₂ toxin precursor. The M₁ (from type 1 yeast killers) and M₂ dsRNA species lack extensive sequence homology, although specific features are shared, which may represent structural elements required for gene expression and replication