McCaffrey G, Clay F J, Kelsay K, Sprague G F
Department of Biology, University of Oregon, Eugene 97403.
Mol Cell Biol. 1987 Aug;7(8):2680-90. doi: 10.1128/mcb.7.8.2680-2690.1987.
We have devised a screen for genes from the yeast Saccharomyces cerevisiae whose expression is affected by cell type or by the mating pheromones. From this screen we identified a gene, FUS1, whose pattern of expression revealed interesting regulatory strategies and whose product was required for efficient cell fusion during mating. Transcription of FUS1 occurred only in a and alpha cells, not in a/alpha cells, where it was repressed by a1 X alpha 2, a regulatory activity present uniquely in a/alpha cells. Transcription of FUS1 showed an absolute requirement for the products of five STE genes, STE4, STE5, STE7, STE11, and STE12. Since the activators STE4, STE5, and STE12 are themselves repressed by a1 X alpha 2, the failure to express FUS1 in a/alpha cells is probably the result of a cascade of regulatory activities; repression of the activators by a1 X alpha 2 in turn precludes transcription of FUS1. In addition to regulation of FUS1 by cell type, transcription from the locus increased 10-fold or more when a or alpha cells were exposed to the opposing mating pheromone. To investigate the function of the Fus1 protein, we created fus1 null mutants. In fus1 X fus1 matings, the cells of a mating pair adhered tightly and appeared to form zygotes. However, the zygotes were abnormal. Within the conjugation bridge the contained a partition that prevented nuclear fusion and mixing of organelles. The predicted sequence of the Fus1 protein (deduced from the FUS1 DNA sequence) and subcellular fractionation studies with Fus1-beta-galactosidase hybrid proteins suggest that Fus1 is a membrane or secreted protein. Thus, Fus1 may be located at a position within the cell where it is poised to catalyze cell wall or plasma membrane fusion.
我们设计了一种筛选方法，用于筛选酿酒酵母中那些表达受细胞类型或交配信息素影响的基因。通过该筛选方法，我们鉴定出了一个基因FUS1，其表达模式揭示了有趣的调控策略，并且其产物是交配过程中细胞高效融合所必需的。FUS1的转录仅发生在a细胞和α细胞中，而在a/α细胞中不发生，在a/α细胞中它被a1×α2抑制，a1×α2是一种仅存在于a/α细胞中的调控活性物质。FUS1的转录对五个STE基因STE4、STE5、STE7、STE11和STE12的产物有绝对需求。由于激活因子STE4、STE5和STE12本身也被a1×α2抑制，所以在a/α细胞中无法表达FUS1可能是一系列调控活动的结果；a1×α2对激活因子的抑制反过来又阻止了FUS1的转录。除了受细胞类型调控外，当a细胞或α细胞暴露于相对的交配信息素时，该基因座的转录增加了10倍或更多。为了研究Fus1蛋白的功能，我们构建了fus1缺失突变体。在fus1×fus1交配中，一对交配细胞紧密粘附，似乎形成了合子。然而，这些合子是异常的。在接合桥内有一个分隔物，阻止了核融合和细胞器的混合。Fus1蛋白的预测序列（从FUS1 DNA序列推导而来）以及用Fus1-β-半乳糖苷酶杂交蛋白进行的亚细胞分级分离研究表明，Fus1是一种膜蛋白或分泌蛋白。因此，Fus1可能位于细胞内的某个位置，随时准备催化细胞壁或质膜融合。
