Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA, 94158, USA.
Nat Commun. 2023 Aug 10;14(1):4848. doi: 10.1038/s41467-023-40485-6.
Binding of transcription factors (TFs) promotes the subsequent recruitment of coactivators and preinitiation complexes to initiate eukaryotic transcription, but this time course is usually not visualized. It is commonly assumed that recruited factors eventually co-reside in a higher-order structure, allowing distantly bound TFs to activate transcription at core promoters. We use live imaging of endogenously tagged proteins, including the pioneer TF Zelda, the coactivator dBrd4, and RNA polymerase II (RNAPII), to define a cascade of events upstream of transcriptional initiation in early Drosophila embryos. These factors are sequentially and transiently recruited to discrete clusters during activation of non-histone genes. Zelda and the acetyltransferase dCBP nucleate dBrd4 clusters, which then trigger pre-transcriptional clustering of RNAPII. Subsequent transcriptional elongation disperses clusters of dBrd4 and RNAPII. Our results suggest that activation of transcription by eukaryotic TFs involves a succession of distinct biomolecular condensates that culminates in a self-limiting burst of transcription.
转录因子 (TFs) 的结合促进了共激活因子和起始前复合物的后续募集，以启动真核转录，但通常无法可视化这个时程。人们通常假设募集的因子最终共同存在于更高阶的结构中，从而允许远距离结合的 TF 在核心启动子处激活转录。我们使用内源性标记蛋白的实时成像，包括先驱 TF Zelda、共激活因子 dBrd4 和 RNA 聚合酶 II (RNAPII)，来定义早期果蝇胚胎中转录起始上游的一系列事件。在非组蛋白基因的激活过程中，这些因子依次短暂地募集到离散的簇中。Zelda 和乙酰转移酶 dCBP 为 dBrd4 簇的形成提供了核心，随后引发了 RNAPII 的转录前簇集。随后的转录延伸会分散 dBrd4 和 RNAPII 的簇。我们的结果表明，真核 TF 激活转录涉及一系列不同的生物分子凝聚物，最终导致自我限制的转录爆发。
