The internal polyadenylate tract of yeast killer virus M₁ double-stranded RNA is variable in length

The 1.8-kbp M₁ double-stranded (ds) RNA from type 1 killer strains of Saccharomyces cerevisiae contains an internal 200-bp adenine- and uracil-rich region. We have previously demonstrated that this region consists primarily of adenine residues on the plus strand of M₁ dsRNA and on the full-length, in vitro synthesized (+) transcript (denoted m) of M₁ dsRNA, neither of which contains 3′-terminal polyadenylate. We now show that there is variability in the length of the polyadenylate tracts of m transcripts synthesized in vitro by virions purified from either of the K₁ diploid killer strains A364A × S7 or A364A × 1384. This variability reflects size differences seen in the corresponding M₁ dsRNA genomes which, along with other data presented, localizes the variability in the length of M₁ dsRNA to the adenine- and uracil-rich region.