Genomic Organization of Human Transcription Initiation Complexes

A repertoire of transcription initiation factors engage the core promoter of mRNA genes to recruit RNA polymerase (Pol) II to initiate transcription, yet their precise spatial organization remains unclear. Using ChIP-exo, here we detail the interactions and genomic organization of initiation factors TBP, TFIIB, and Pol II at mRNA genes and within CpG islands. We find that when Pol II moves into a transcriptionally paused state, TBP/TFIIB remain at the promoter. We show that TBP and TFIIB bound to the core promoter at two separate, resolvable locations that coincided with sites of divergent transcription initiation. We also examine the precise binding of TBP at Pol III transcribed tRNA genes. We find that TBP crosslinked to tRNA genes in a similar manner as at Pol II transcribed genes. This comprehensive and high resolution genome-wide detection of the initiation machinery produces a consolidated view of transcription initiation events humans at Pol II coding and Pol III transcribed tRNA genes.多种转录起始因子结合mRNA基因的核心启动子，招募RNA聚合酶II（Pol II）以启动转录，但其精确的空间组织形式仍有待阐明。本研究借助染色质免疫沉淀-外切酶测序（ChIP-exo）技术，详细解析了mRNA基因及CpG岛（CpG islands）内的转录起始因子TATA盒结合蛋白（TBP）、转录因子IIB（TFIIB）与Pol II的相互作用及其基因组组织模式。我们发现，当Pol II进入转录暂停状态时，TBP与TFIIB仍驻留于启动子区域。研究表明，结合于核心启动子的TBP与TFIIB分别位于两个可分辨的独立位点，且与双向转录起始位点相吻合。我们同时检测了TBP在RNA聚合酶III（Pol III）转录的tRNA基因上的精确结合特征。结果显示，TBP在tRNA基因上的交联模式与Pol II转录的基因高度相似。本研究通过高分辨率全基因组检测转录起始机器，为Pol II编码基因及Pol III转录的tRNA基因的转录起始事件提供了整合性认知。