Tzamarias D, Struhl K
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115.
Nature. 1994 Jun 30;369(6483):758-61. doi: 10.1038/369758a0.
DNA-binding repressor proteins mediate regulation of yeast genes by cell type (Mcm1/alpha 2 and a1/alpha 2), glucose (Mig1) and oxygen (Rox1) (refs 1-4 respectively). An unusual feature of all these regulatory pathways is that transcriptional repression requires two physically associated proteins that do not bind DNA Cyc8(Ssn6) and Tup1. The Cyc8-Tup1 complex has been proposed to be a co-repressor that is recruited to target promoters by pathway-specific DNA-binding proteins, but the specific functions of the individual proteins are unknown. Here we show that when it is bound upstream of a functional promoter through the LexA DNA-binding domain, Tup1 represses transcription in the absence of Cyc8. Deletion analysis indicates that Tup1 contains at least two non-overlapping transcriptional repression regions with minimal primary sequence similarity, and a separable Cyc8-interaction domain. These Tup1 domains, which do not include the beta-transducin motifs, are necessary and partially sufficient for Tup1 function. We suggest that Tup1 performs the repression function of the Cyc8-Tup1 co-repressor complex, and that Cyc8 serves as a link with the pathway-specific DNA-binding proteins.
DNA结合阻遏蛋白介导酵母基因受细胞类型（Mcm1/α2和a1/α2）、葡萄糖（Mig1）和氧气（Rox1）的调控（分别参考文献1 - 4）。所有这些调控途径的一个不同寻常的特点是，转录抑制需要两种不结合DNA的物理结合蛋白Cyc8（Ssn6）和Tup1。有人提出Cyc8 - Tup1复合物是一种共阻遏物，它由途径特异性DNA结合蛋白招募到靶启动子，但单个蛋白的具体功能尚不清楚。在这里我们表明，当Tup1通过LexA DNA结合结构域结合在功能启动子上游时，在没有Cyc8的情况下它也能抑制转录。缺失分析表明，Tup1包含至少两个不重叠的转录抑制区域，其一级序列相似性最小，还有一个可分离的Cyc8相互作用结构域。这些Tup1结构域不包括β - 转导蛋白基序，对Tup1功能是必需的且部分是充分的。我们认为Tup1执行Cyc8 - Tup1共阻遏物复合物的抑制功能，而Cyc8作为与途径特异性DNA结合蛋白的连接物。
