Leibowitz M J, Wickner R B
Proc Natl Acad Sci U S A. 1976 Jun;73(6):2061-5. doi: 10.1073/pnas.73.6.2061.
"Killer" strains of Saccharomyces cerevisiae are those that harbor a double-stranded RNA plasmid and secrete a toxin that kills only strains not carrying this plasmid (sensitives). Two chromosomal genes (kex1 and kex2) are required for the secretion of toxin by plasmid-carrying strains. The kex2 gene, which maps at a site distinct from the mating-type locus, is also required for normal mating by alpha strains and meiotic sporulation in all strains. Strains that are alpha mating-type and kex2 fail to secrete the pheromone alpha-factor or to respond to the alpha-factor II pheromone which causes a morphological change, but they do respond to alpha-factor I which causes G1 arrest in alpha cells. Strains that are alpha mating-type and kex2 show no defect in mating; pheromone secretion, or response to alpha-factor. Diploids that are homozygous for the kex2 mutation, unlike wildtype or heterozygous diploids, fail to undergo sporulation, with the defect occurring in the final spore maturation stage. These same defects in the sexual cycle are present in all kex2 mutants independent of the presence of the "killer" plasmid.
酿酒酵母的“杀手”菌株是那些携带双链RNA质粒并分泌一种毒素的菌株，这种毒素只会杀死不携带该质粒的菌株（敏感菌株）。携带质粒的菌株分泌毒素需要两个染色体基因（kex1和kex2）。kex2基因定位于与交配型位点不同的位置，α菌株正常交配以及所有菌株减数分裂产孢也需要该基因。α交配型且kex2缺陷的菌株无法分泌信息素α因子，也无法对引起形态变化的α因子II信息素作出反应，但它们对引起α细胞G1期停滞的α因子I有反应。α交配型且kex2缺陷的菌株在交配、信息素分泌或对α因子的反应方面没有缺陷。与野生型或杂合二倍体不同，kex2突变纯合的二倍体无法进行孢子形成，缺陷发生在最终的孢子成熟阶段。所有kex2突变体在有性生殖周期中都存在这些相同的缺陷，与“杀手”质粒的存在无关。
