Lee Y C, Kim Y J
Laboratory of Molecular Genetics, Center for Molecular Medicine, Samsung Biomedical Research Institute, Kangnam-ku, Seoul 135-230, Korea.
Mol Cell Biol. 1998 Sep;18(9):5364-70. doi: 10.1128/MCB.18.9.5364.
Regulated transcription of class II genes of the yeast Saccharomyces cerevisiae requires the diverse functions of mediator complex. In particular, MED6 is essential for activated transcription from many class II promoters, suggesting that it functions as a key player in the relay of activator signals to the basal transcription machinery. To identify the functional relationship between MED6 and other transcriptional regulators, we conducted a genetic screen to isolate a suppressor of a temperature-sensitive (ts) med6 mutation. We identified an SRB4 allele as a dominant and allele-specific suppressor of med6-ts. A single missense mutation in SRB4 can specifically suppress transcriptional defects caused by the med6 ts mutation, indicating a functional interaction between these two mediator subunits in the activation of transcription. Biochemical analysis of mediator subassembly revealed that mediator can be dissociated into two tightly associated subcomplexes. The Med6 and Srb4 proteins are contained in the same subcomplex together with other dominant Srb proteins, consistent with their functional relationship revealed by the genetic study. Our results suggest not only the existence of a specific interaction between Med6 and Srb4 but also the requirement of this interaction in transcriptional regulation of RNA polymerase II holoenzyme.
酿酒酵母II类基因的转录调控需要中介体复合物的多种功能。特别是，MED6对于许多II类启动子的激活转录至关重要，这表明它在激活子信号传递至基础转录机制的过程中起关键作用。为了确定MED6与其他转录调节因子之间的功能关系，我们进行了遗传筛选以分离温度敏感型（ts）med6突变的抑制子。我们鉴定出一个SRB4等位基因作为med6-ts的显性且等位基因特异性抑制子。SRB4中的单个错义突变可以特异性地抑制由med6 ts突变引起的转录缺陷，这表明这两个中介体亚基在转录激活中存在功能相互作用。对中介体亚组件的生化分析表明，中介体可以解离为两个紧密相关的亚复合物。Med6和Srb4蛋白与其他显性Srb蛋白一起包含在同一亚复合物中，这与其遗传研究揭示的功能关系一致。我们的结果不仅表明Med6和Srb4之间存在特定相互作用，而且还表明这种相互作用在RNA聚合酶II全酶的转录调控中是必需的。
