Haploid cells of the budding yeast Saccharomyces cerevisiae communicate using secreted pheromones and mate to form diploid zygotes. Mating is monogamous, resulting in the fusion of precisely one cell of each mating type. Monogamous mating in crowded conditions, where cells have access to more than one potential partner, raises the question of how multiple-mating outcomes are prevented. Here we identify mutants capable of mating with multiple partners, revealing the mechanisms that ensure monogamous mating. Before fusion, cells develop polarity foci oriented towards potential partners. Competition between these polarity foci within each cell leads to disassembly of all but one focus, thus favoring a single fusion event. Fusion promotes the formation of heterodimeric complexes between subunits that are uniquely expressed in each mating type. One complex shuts off haploid-specific gene expression, and the other shuts off the ability to respond to pheromone. Zygotes able to form either complex remain monogamous, but zygotes lacking both can re-mate.

出芽酵母酿酒酵母的单倍体细胞使用分泌的信息素和交配形成二倍体受精卵进行交流。交配是一夫一妻制，导致每种交配类型的细胞精确融合。在拥挤的条件下进行一夫一妻制交配，在这种情况下，细胞可以接触到一个以上的潜在伴侣，这就提出了如何防止多重交配结果的问题。在这里，我们确定了能够与多个伴侣交配的突变体，揭示了确保一夫一妻制交配的机制。在融合之前，细胞会发展出面向潜在伙伴的极性焦点。每个细胞内这些极性焦点之间的竞争导致除一个焦点之外的所有焦点的分解，从而有利于单个融合事件。融合促进在每个交配类型中独特表达的亚基之间形成异二聚体复合物。一种复合物关闭单倍体特异性基因表达，另一个关闭对信息素作出反应的能力。能够形成任一复合体的受精卵保持一夫一妻制，但缺乏两者的受精卵可以重新交配。