PREPONDERANCE OF FREE MEDIATOR IN THE YEAST SACCHAROMYCES CEREVISIAE

该子项目是利用NIH/NCRR资助的中心赠款提供的资源的许多研究子项目之一。子项目和研究者（PI）可能从另一个NIH来源获得主要资金，因此可以在其他CRISP条目中表示。所列机构为中心，不一定是研究者所在机构。生化证据表明，在酵母酿酒酵母中的主要形式的调解人可能是一个复杂的是与RNA聚合酶II形成全酶，导致了一个全酶为基础的转录起始模型的命题。我们报告说，无聚合酶的介体，分离早期的全细胞提取物分馏协议，实际上是最丰富的形式的介体复合物。游离介体的存在使得介体和RNA聚合酶II独立募集到前起始复合物成为可能。这是在协议的时间和空间的独立性的介质和RNA聚合酶II启动子相互作用的体内研究的报告，与当前模型的preinitiation复杂的结构，其中启动子DNA上游的转录起始位点位于介质和聚合酶之间，并与建议的作用的介质作为主要组成部分的支架复合物参与转录再起始。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Biochemical evidence suggesting that the predominant form of Mediator in the yeast Saccharomyces cerevisiae might be one in which the complex is associated with RNA polymerase II to form a holoenzyme has led to the proposition of a holoenzyme-based model for transcription initiation. We report that polymerase-free Mediator, isolated early on during a whole-cell extract fractionation protocol, is in fact the most abundant form of the Mediator complex. The existence of free Mediator would make possible independent recruitment of Mediator and RNA polymerase II to the preinitiation complex. This is in agreement with reports from in vivo studies of time and spatial independence of Mediator and RNA polymerase II promoter interaction, with current models of preinitiation complex structure in which promoter DNA upstream of the transcription start site is positioned between Mediator and polymerase, and with the proposed role of Mediator as the major component of the Scaffold complex involved in transcription reinitiation.