Twenty-six chromosomal genes needed to maintain the killer double-stranded RNA plasmid of Saccharomyces cerevisiae.

The double-stranded RNA killer plasmid gives yeast strains carrying it both the ability to secret a protein toxin and immunity to that toxin. This report describes a new series of mutants in chromsomal genes needed for killer plasmid maintenance (mak genes). These mutants comprise 12 complementation groups. There are a total of at least 26 mak genes. Each mak gene product is needed for plasmid maintenance in diploids as well as in haploids. None of these mak mutations prevent the killer plasmid from entering the mak- spores in the process of meiotic sporulation. Complementation between mak mutants can be performed by mating meitoic spores from a makx/+ plasmid-carrying diploid with a maky haploid. If x = y, about half the diploid clones formed lose the killer plasmid. If x not equal to y, complementation occurs, and all of the diploid clones are killers.