Yeast Killer Mutants with Altered Double-Stranded Ribonucleic Acid

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Killer strains of Saccharomyces cerevisiae contain two species of double-stranded ribonucleic acid (dsRNA) with molecular weights estimated at 2.5 × 106 (L) and 1.4 × 106 (M). The M component appears to have a high adenine content. All mutants of killer which are defective for both the toxin and immunity functions lack the M dsRNA. One of these mutants has a novel dsRNA with a molecular weight of 5 × 105. Another class of killer mutants contains strains which are defective for either the toxin or the immunity function. They include temperature-sensitive killers, superkillers, and immunity-minus strains. The dsRNA profile of temperature-sensitive killers resembles that of the standard killer. The superkiller has 2.5 times more of the M dsRNA (1.4 × 106 daltons) than does the standard killer. Immunity-minus killers have, in addition to the two dsRNAs species of standard killer, a novel dsRNA with a molecular weight of 2.5 × 105. The data are consistent with the hypothesis that the M RNA controls toxin production. In addition, the two RNAs, L and M, seem to be regulated together. When the M RNA is missing, the amount of L is either greatly elevated or greatly reduced.

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