Abstract：
RNA polymerase II (Pol II)-mediated transcription in metazoans requires precise regulation. RNA Pol II-associated protein 2 (RPAP2) was previously identified to transport Pol II from cytoplasm to nucleus and dephosphorylates Pol II C-terminal domain (CTD). Here, we show that RPAP2 binds hypo-/hyper-phosphorylated Pol II with undetectable phosphatase activity. The structure of RPAP2-Pol II shows mutually exclusive assembly of RPAP2-Pol II and pre-initiation complex (PIC) due to three steric clashes. RPAP2 prevents and disrupts Pol II-TFIIF interaction and impairs in vitro transcription initiation, suggesting a function in inhibiting PIC assembly. Loss of RPAP2 in cells leads to global accumulation of TFIIF and Pol II at promoters, indicating a critical role of RPAP2 in inhibiting PIC assembly independent of its putative phosphatase activity. Our study indicates that RPAP2 functions as a gatekeeper to inhibit PIC assembly and transcription initiation and suggests a transcription checkpoint.
摘要：
在后生动物中RNA聚合酶II（PolII）介导的转录需要精确调节。RNAPolII相关蛋白2（RPAP2）先前被鉴定为将PolII从细胞质转运到细胞核，并使PolIIC末端结构域（CTD）去磷酸化。这里,我们显示RPAP2结合低/高磷酸化PolII,磷酸酶活性检测不到.由于三个空间冲突，RPAP2-PolII的结构显示了RPAP2-PolII和预起始复合物（PIC）的互斥组装。RPAP2阻止和破坏PolII-TFIIF相互作用并损害体外转录起始，表明抑制PIC组装的功能。细胞中RPAP2的缺失导致TFIIF和PolII在启动子处的整体积累,表明RPAP2在抑制PIC组装中的关键作用，而与其推定的磷酸酶活性无关。我们的研究表明，RPAP2作为看门人抑制PIC组装和转录起始，并提出了转录检查点。
