RNA polymerase I (Pol I) transcription takes place at the border of the fibrillar center (FC) and the dense fibrillar component (DFC) in the nucleolus. Here, we report that individual spherical FC/DFC units are coated by the DEAD-box RNA helicase DDX21 in human cells. The long noncoding RNA (lncRNA) SLERT binds to DDX21 RecA domains to promote DDX21 to adopt a closed conformation at a substoichiometric ratio through a molecular chaperone–like mechanism resulting in the formation of hypomultimerized and loose DDX21 clusters that coat DFCs, which is required for proper FC/DFC liquidity and Pol I processivity. Our results suggest that SLERT is an RNA regulator that controls the biophysical properties of FC/DFCs and thus ribosomal RNA production.

RNA 聚合酶 I (Pol I) 转录发生在核仁中的纤维中心 (FC) 和致密纤维成分 (DFC) 的边界。在这里，我们报告了单个球形 FC/DFC 单元在人类细胞中被 DEAD-box RNA 解旋酶 DDX21 包被。长非编码RNA（lncRNA）SLERT结合于DDX21 RecA的结构域以促进DDX21通过采用以亚化学计量比的闭合构象的分子伴侣样导致hypomultimerized和松散DDX21簇的形成机制，涂层牙囊，这是需要适当的 FC/DFC 流动性和 Pol I 处理能力。我们的研究结果表明，SLERT是一种 RNA 调节剂，可控制 FC/DFC 的生物物理特性，从而控制核糖体 RNA 的产生。