Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Mol Cell. 2018 Feb 15;69(4):648-663.e7. doi: 10.1016/j.molcel.2018.01.006. Epub 2018 Feb 1.
Regulation of RNA polymerase II (Pol II) elongation is a critical step in gene regulation. Here, we report that U1 snRNP recognition and transcription pausing at stable nucleosomes are linked through premature polyadenylation signal (PAS) termination. By generating RNA exosome conditional deletion mouse embryonic stem cells, we identified a large class of polyadenylated short transcripts in the sense direction destabilized by the RNA exosome. These PAS termination events are enriched at the first few stable nucleosomes flanking CpG islands and suppressed by U1 snRNP. Thus, promoter-proximal Pol II pausing consists of two processes: TSS-proximal and +1 stable nucleosome pausing, with PAS termination coinciding with the latter. While pausing factors NELF/DSIF only function in the former step, flavopiridol-sensitive mechanism(s) and Myc modulate both steps. We propose that premature PAS termination near the nucleosome-associated pause site represents a common transcriptional elongation checkpoint regulated by U1 snRNP recognition, nucleosome stability, and Myc activity.
RNA 聚合酶 II（Pol II）延伸的调控是基因调控的关键步骤。在这里，我们报告说，U1 小核核糖核蛋白（snRNP）的识别与在稳定核小体上的转录暂停通过过早的多聚腺苷酸化信号（PAS）终止相联系。通过生成 RNA 外切酶条件性缺失的小鼠胚胎干细胞，我们在正义链上鉴定到一大类由 RNA 外切酶稳定的多聚腺苷酸化的短转录本。这些 PAS 终止事件在侧翼 CpG 岛的前几个稳定核小体处富集，并受到 U1 snRNP 的抑制。因此，启动子近端 Pol II 暂停由两个过程组成：TSS 近端和+1 稳定核小体暂停，PAS 终止与后者重合。虽然暂停因子 NELF/DSIF 仅在前一个步骤中起作用，但 flavopiridol 敏感的机制和 Myc 调节这两个步骤。我们提出，在与核小体相关的暂停位点附近的过早 PAS 终止代表了一个受 U1 snRNP 识别、核小体稳定性和 Myc 活性调节的常见转录延伸检查点。
