Liu Zhongle, Myers Lawrence C
Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire, United States of America.
PLoS One. 2012;7(6):e38416. doi: 10.1371/journal.pone.0038416. Epub 2012 Jun 5.
The Mediator complex transmits activation signals from DNA bound transcription factors to the core transcription machinery. In addition to its canonical role in transcriptional activation, recent studies have demonstrated that S. cerevisiae Mediator can interact directly with nucleosomes, and their histone tails. Mutations in Mediator subunits have shown that Mediator and certain chromatin structures mutually impact each other structurally and functionally in vivo. We have taken a UV photo cross-linking approach to further delineate the molecular basis of Mediator chromatin interactions and help determine whether the impact of certain Mediator mutants on chromatin is direct. Specifically, by using histone tail peptides substituted with an amino acid analog that is a UV activatible crosslinker, we have identified specific subunits within Mediator that participate in histone tail interactions. Using Mediator purified from mutant yeast strains we have evaluated the impact of these subunits on histone tail binding. This analysis has identified the Med5 subunit of Mediator as a target for histone tail interactions and suggests that the previously observed effect of med5 mutations on telomeric heterochromatin and silencing is direct.
中介体复合物将来自与DNA结合的转录因子的激活信号传递给核心转录机制。除了其在转录激活中的经典作用外，最近的研究表明，酿酒酵母中介体可以直接与核小体及其组蛋白尾巴相互作用。中介体亚基的突变表明，中介体和某些染色质结构在体内的结构和功能上相互影响。我们采用了紫外线光交联方法来进一步阐明中介体与染色质相互作用的分子基础，并帮助确定某些中介体突变体对染色质的影响是否是直接的。具体而言，通过使用用作为紫外线可激活交联剂的氨基酸类似物取代的组蛋白尾巴肽，我们已经确定了中介体内参与组蛋白尾巴相互作用的特定亚基。使用从突变酵母菌株中纯化的中介体，我们评估了这些亚基对组蛋白尾巴结合的影响。该分析已确定中介体的Med5亚基是组蛋白尾巴相互作用的靶点，并表明先前观察到的med5突变对端粒异染色质和沉默的影响是直接的。
