Establishment of B-lineage-specific gene expression requires the binding of transcription factors to inaccessible chromatin of progenitors. The transcription factor EBF1 can bind genomic regions prior to the detection of chromatin accessibility in a manner dependent on EBF1’s C-terminal domain (CTD) and independent of cooperating transcription factors. Here, we studied the mechanism whereby the CTD enables this pioneering function. The CTD of EBF1 was dispensable for initial chromatin targeting but stabilized occupancy via recruitment of the chromatin remodeler Brg1. We found that the CTD harbors a prion-like domain (PLD) with an ability of liquid-liquid phase separation, which was enhanced by interaction of EBF1 with the RNA-binding protein FUS. Brg1 also partitioned into phase-separated FUS condensates and coincided with EBF1 and FUS foci in pro-B cells. Heterologous PLDs conferred pioneering function on EBF1ΔCTD. Thus, the phase separation ability of EBF1 facilitates Brg1-mediated chromatin opening and the transition of naive progenitor chromatin to B-lineage-committed chromatin.

B谱系特异性基因表达的建立需要转录因子与祖细胞难以获得的染色质结合。在检测染色质可及性之前，转录因子EBF1可以结合基因组区域，其方式取决于EBF1的C末端结构域（CTD），而与合作的转录因子无关。在这里，我们研究了CTD启用此先驱功能的机制。EBF1的CTD可用于初始染色质靶向，但可通过募集染色质重塑剂Brg1来稳定占用。我们发现CTD带有一个a液样结构域（PLD），具有液相-液相分离的能力，这是通过EBF1与RNA结合蛋白FUS的相互作用而增强的。Brg1也被分隔成相分离的FUS冷凝物，并与pro-B细胞中的EBF1和FUS灶相吻合。异源PLD赋予EBF1ΔCTD开拓性功能。因此，EBF1的相分离能力促进了Brg1介导的染色质的开放和幼稚祖细胞染色质向B谱系所定染色质的过渡。