Maisonneuve-Rosemont Hospital, Research Center, Department of Immunology and Oncology, University of Montreal, 5415 de l'Assomption, Montreal, Quebec, Canada.
BMC Mol Biol. 2010 Dec 3;11:92. doi: 10.1186/1471-2199-11-92.
In Saccharomyces cerevisiae, the immunosuppressant rapamycin engenders a profound modification in the transcriptional profile leading to growth arrest. Mutants devoid of Rrd1, a protein possessing in vitro peptidyl prolyl cis/trans isomerase activity, display striking resistance to the drug, although how Rrd1 activity is linked to the biological responses has not been elucidated.
We now provide evidence that Rrd1 is associated with the chromatin and it interacts with RNA polymerase II. Circular dichroism revealed that Rrd1 mediates structural changes onto the C-terminal domain (CTD) of the large subunit of RNA polymerase II (Rpb1) in response to rapamycin, although this appears to be independent of the overall phosphorylation status of the CTD. In vitro experiments, showed that recombinant Rrd1 directly isomerizes purified GST-CTD and that it releases RNA polymerase II from the chromatin. Consistent with this, we demonstrated that Rrd1 is required to alter RNA polymerase II occupancy on rapamycin responsive genes.
We propose as a mechanism, that upon rapamycin exposure Rrd1 isomerizes Rpb1 to promote its dissociation from the chromatin in order to modulate transcription.
在酿酒酵母中，免疫抑制剂雷帕霉素会导致转录谱发生深刻改变，从而导致生长停滞。缺乏 Rrd1 的突变体缺乏体外肽基脯氨酰顺/反异构酶活性，对药物表现出明显的抗性，尽管 Rrd1 活性与生物反应如何联系尚未阐明。
我们现在提供的证据表明，Rrd1 与染色质相关，并与 RNA 聚合酶 II 相互作用。圆二色性显示，Rrd1 响应雷帕霉素介导 RNA 聚合酶 II 大亚基（Rpb1）C 末端结构域（CTD）的结构变化，尽管这似乎独立于 CTD 的整体磷酸化状态。体外实验表明，重组 Rrd1 可直接使 GST-CTD 异构化，并使 RNA 聚合酶 II 从染色质中释放出来。与此一致，我们证明 Rrd1 是改变 RNA 聚合酶 II 在雷帕霉素反应基因上的占据所必需的。
我们提出了一种机制，即在雷帕霉素暴露时，Rrd1 使 Rpb1 异构化，以促进其从染色质中解离，从而调节转录。
