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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Identification of a regulator of transcription elongation as an accessory factor for the human Mediator coactivator
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Identification of a regulator of transcription elongation as an accessory factor for the human Mediator coactivator

机译：鉴定转录延长调控因子作为人类Mediator共激活因子的辅助因子

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摘要

The multiprotein Mediator coactivator complex is universally required for transcription of metazoan genes. It has been proposed to function by interfacing between transcriptional activators and the RNA polymerase Ⅱ machinery. However, in vitro transcription systems reconstituted from homogeneous preparations of RNA polymerase Ⅱ, the general transcription initiation factors, and the cofactor PC4 display relatively robust activator (HNF-4)-dependent activity, which, nonetheless, can be further stimulated by Mediator. By contrast, an unfractionated nuclear extract-based system in which Mediator has been immunodepleted displays a near-absolute dependence on ectopic Mediator. Here, we identified and purified an activity, MSA-2, that confers extract-like Mediator responsiveness to our reconstituted system. Mass spectrometric analyses identified its two constituent polypeptides as hSpt5 and hSpt4, which also comprise the elongation factor DSIF. Mechanistically, MSA-2/DSIF acts by restricting overall transcription in the pure system, thereby imposing a strong Mediator dependence. Our data thus point to potential mechanisms for Mediator function beyond its presently believed role in promoting the initial formation of the RNA polymerase Ⅱ-containing preinitiation complex.
机译：后生动物基因转录普遍需要多蛋白介体共激活物复合物。已经提出通过转录激活因子和RNA聚合酶Ⅱ机制之间的接口来发挥作用。然而，由RNA聚合酶Ⅱ的均质制剂，一般的转录起始因子和辅因子PC4重建的体外转录系统显示出相对强健的激活因子（HNF-4）依赖性活性，尽管如此，它仍可以被介体进一步刺激。相比之下，Mediator已被免疫耗竭的基于普通核提取物的系统显示出几乎完全依赖于异位Mediator。在这里，我们鉴定并纯化了一种活性MSA-2，该活性赋予提取物样介体对我们重构系统的响应能力。质谱分析确定了它的两个组成多肽，即hSpt5和hSpt4，它们也包含延伸因子DSIF。从机理上讲，MSA-2 / DSIF通过限制纯系统中的总体转录来发挥作用，从而强加了介体依赖性。因此，我们的数据指出了介体功能的潜在机制，超出了其目前认为的促进含RNA聚合酶Ⅱ的预启动复合物初始形成的作用。

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