Yeast Killer Mutants with Altered Double-Stranded Ribonucleic Acid

Abstract

Killer strains of Saccharomyces cerevisiae contain two species of double-stranded ribonucleic acid ( ds RNA) with molecular weights estimated at 2.5 × 10 6 ( L ) and 1.4 × 10 6 ( 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 ds RNA. One of these mutants has a novel ds RNA with a molecular weight of 5 × 10 5 . 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 ds RNA profile of temperature-sensitive killers resembles that of the standard killer. The superkiller has 2.5 times more of the M ds RNA (1.4 × 10 6 daltons) than does the standard killer. Immunity-minus killers have, in addition to the two ds RNAs species of standard killer, a novel ds RNA with a molecular weight of 2.5 × 10 5 . 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.