PREPONDERANCE OF FREE MEDIATOR IN THE YEAST SACCHAROMYCES CEREVISIAE

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。生化证据表明，酿酒酵母中的主要介体形式可能是复合体与RNA聚合酶II结合形成全酶，这导致了基于全酶的转录启动模型的提出。我们报告说，早期在全细胞提取分离过程中分离出来的无聚合酶介体实际上是介体复合体中最丰富的形式。自由介体的存在将使介体和RNA聚合酶II独立地招募到起始前复合体中。这与体内对介体和RNA聚合酶II启动子相互作用的时间和空间独立性的研究报告一致，与目前转录起始点上游启动子DNA位于介体和聚合酶之间的预起始复合体结构模型相一致，并与介体作为参与转录再起始的支架复合体的主要组成部分的提议一致。

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.