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Two chromosomal genes required for killing expression in killer strains of Saccharomyces cerevisiae

R B Wickner, M J Leibowitz

    Genetics
    |March 25, 1976
    PubMed

    Insights

    Yeast killer toxin production relies on a double-stranded RNA plasmid and chromosomal genes. Researchers identified two new genes, KEX1 and KEX2, crucial for toxin secretion, revealing insights into yeast killer character.

    Area of Science:

    • Microbiology
    • Genetics
    • Molecular Biology

    Background:

    • Yeast killer character is determined by a double-stranded RNA plasmid and chromosomal genes.
    • Killer yeast strains secrete a toxin lethal to sensitive strains lacking the plasmid.

    Purpose of the Study:

    • To isolate and characterize chromosomal mutants affecting yeast killer toxin secretion.
    • To identify and map genes involved in the killer phenotype.

    Main Methods:

    • Isolation of recessive chromosomal mutants from a killer yeast strain.
    • Complementation analysis to define complementation groups.
    • Genetic mapping of mutations to specific chromosomes.
    • Curing experiments to assess plasmid dependence.
    • Analysis of double-stranded RNA levels.

    Main Results:

    • 28 independent recessive mutants were isolated, defining two complementation groups: kex1 and kex2.
    • Kex1 mutants mapped to chromosome VII, and Kex2 mutants to chromosome XIV.
    • Mutant phenotypes were independent of killer plasmid alteration.
    • kex1 and kex2 strains maintained near-normal levels of the killer plasmid double-stranded RNA.

    Conclusions:

    • The kex1 and kex2 genes are essential for the secretion of active killer toxin in yeast.
    • These genes are chromosomal and do not require direct alteration of the killer plasmid for their function.
    • The identified genes provide new insights into the genetic control of yeast killer phenotypes.

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