Department of Biology, Johns Hopkins University, Baltimore, MD, USA.
Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, USA.
Nat Struct Mol Biol. 2022 Jul;29(7):665-676. doi: 10.1038/s41594-022-00800-z. Epub 2022 Jul 14.
How pioneer factors interface with chromatin to promote accessibility for transcription control is poorly understood in vivo. Here, we directly visualize chromatin association by the prototypical GAGA pioneer factor (GAF) in live Drosophila hemocytes. Single-particle tracking reveals that most GAF is chromatin bound, with a stable-binding fraction showing nucleosome-like confinement residing on chromatin for more than 2 min, far longer than the dynamic range of most transcription factors. These kinetic properties require the full complement of GAF's DNA-binding, multimerization and intrinsically disordered domains, and are autonomous from recruited chromatin remodelers NURF and PBAP, whose activities primarily benefit GAF's neighbors such as Heat Shock Factor. Evaluation of GAF kinetics together with its endogenous abundance indicates that, despite on-off dynamics, GAF constitutively and fully occupies major chromatin targets, thereby providing a temporal mechanism that sustains open chromatin for transcriptional responses to homeostatic, environmental and developmental signals.
在体内，先驱因子如何与染色质相互作用以促进转录调控的可及性还知之甚少。在这里，我们在活的果蝇血细胞中直接可视化原型 GAGA 先驱因子 (GAF) 与染色质的关联。单颗粒跟踪显示，大多数 GAF 与染色质结合，具有稳定结合分数的部分表现出类似于核小体的限制，位于染色质上超过 2 分钟，远远超过大多数转录因子的动态范围。这些动力学特性需要 GAF 的 DNA 结合、多聚化和固有无序结构域的完整互补，并且与募集的染色质重塑因子 NURF 和 PBAP 无关，其活性主要有利于 GAF 的邻居，如热休克因子。对 GAF 动力学及其内源性丰度的评估表明，尽管存在开-关动力学，但 GAF 持续且完全占据主要的染色质靶标，从而提供了一种时间机制，维持开放染色质，以响应稳态、环境和发育信号的转录反应。
