Department of Microbiology and Molecular Medicine, University Medical Centre (C.M.U.), 1211 Geneva 4, Switzerland.
Genome Res. 2014 Jan;24(1):117-24. doi: 10.1101/gr.157792.113. Epub 2013 Dec 2.
Transcription by all three eukaryotic RNA polymerases involves the assembly of a large preinitiation complex (PIC) at gene promoters. The PIC comprises several general transcription factors (GTFs), including TBP, and the respective RNA polymerase. It has been suggested that some GTFs remain stably bound at active promoters to facilitate multiple transcription events. Here we used two complementary approaches to show that, in G1-arrested yeast cells, TBP exchanges very rapidly even at the most highly active RNA Pol II promoters. A similar situation is observed at RNA Pol III promoters. In contrast, TBP remains stably bound at RNA Pol I promoters. We also provide evidence that, unexpectedly, PIC dynamics are neither the cause nor the consequence of nucleosome exchange at most of the RNA Pol II promoters we analyzed. These results point to a stable reinitiation complex at RNA Pol I promoters and suggest independent PIC and nucleosome turnover at many RNA Pol II promoters.
真核生物的三种 RNA 聚合酶的转录都涉及在基因启动子处组装一个大型起始前复合物（PIC）。PIC 包含几个一般转录因子（GTF），包括 TBP 和相应的 RNA 聚合酶。有人提出，一些 GTF 在活跃的启动子处保持稳定结合，以促进多个转录事件。在这里，我们使用两种互补的方法表明，在 G1 期被阻断的酵母细胞中，TBP 甚至在最活跃的 RNA Pol II 启动子处也能快速交换。在 RNA Pol III 启动子上也观察到类似的情况。相比之下，TBP 在 RNA Pol I 启动子处保持稳定结合。我们还提供了证据表明，出乎意料的是，在我们分析的大多数 RNA Pol II 启动子上，PIC 动力学既不是核小体交换的原因，也不是其结果。这些结果表明，在 RNA Pol I 启动子处存在稳定的重新起始复合物，并表明在许多 RNA Pol II 启动子处，PIC 和核小体周转是独立的。
