RNA-dependent chromatin association of transcription elongation factors and Pol II CTD kinases

For transcription through chromatin, RNA polymerase (Pol) II associates with elongation factors (EFs). Here we show that many EFs crosslink to RNA emerging from transcribing Pol II in the yeast Saccharomyces cerevisiae. Most EFs crosslink preferentially to mRNAs, rather than unstable non-coding RNAs. RNA contributes to chromatin association of many EFs, including the Pol II serine 2 kinases Ctk1 and Bur1 and the histone H3 methyltransferases Set1 and Set2. The Ctk1 kinase complex binds RNA in vitro , consistent with direct EF-RNA interaction. Set1 recruitment to genes in vivo depends on its RNA recognition motifs (RRMs). These results strongly suggest that nascent RNA contributes to EF recruitment to transcribing Pol II. We propose that EF-RNA interactions facilitate assembly of the elongation complex on transcribed genes when RNA emerges from Pol II, and that loss of EF-RNA interactions upon RNA cleavage at the polyadenylation site triggers disassembly of the elongation complex.在染色质转录过程中，RNA聚合酶II（RNA polymerase (Pol) II）可与延伸因子（elongation factors，EFs）相结合。本研究以酿酒酵母（Saccharomyces cerevisiae）为研究对象，证实众多延伸因子可与转录中的Pol II所延伸出的RNA发生交联。大多数延伸因子优先与信使RNA（mRNA）结合，而非不稳定的非编码RNA。RNA可促进众多延伸因子与染色质的结合，其中包括Pol II丝氨酸2激酶Ctk1、Bur1以及组蛋白H3甲基转移酶Set1和Set2。体外实验表明，Ctk1激酶复合物可直接结合RNA，这与延伸因子与RNA的直接相互作用结论一致。体内实验中，Set1被招募至基因位点的过程依赖于其RNA识别基序（RNA recognition motifs，RRMs）。上述结果有力表明，新生RNA可促进延伸因子被招募至转录中的Pol II。我们提出，当RNA从Pol II中延伸出来时，延伸因子与RNA的相互作用可促进转录基因上延伸复合物的组装；而在多聚腺苷酸化位点发生RNA切割后，延伸因子与RNA的相互作用丧失，会触发延伸复合物的解聚。