Liquid–liquid phase separation is a major mechanism of subcellular compartmentalization^1,2. Although the segregation of RNA into phase-separated condensates broadly affects RNA metabolism^3,4, whether and how specific RNAs use phase separation to regulate interacting factors such as RNA-binding proteins (RBPs), and the phenotypic consequences of such regulatory interactions, are poorly understood. Here we show that RNA-driven phase separation is a key mechanism through which a long noncoding RNA (lncRNA) controls the activity of RBPs and maintains genomic stability in mammalian cells. The lncRNA NORAD prevents aberrant mitosis by inhibiting Pumilio (PUM) proteins^5,6,7,8. We show that NORAD can out-compete thousands of other PUM-binding transcripts to inhibit PUM by nucleating the formation of phase-separated PUM condensates, termed NP bodies. Dual mechanisms of PUM recruitment, involving multivalent PUM–NORAD and PUM–PUM interactions, enable NORAD to competitively sequester a super-stoichiometric amount of PUM in NP bodies. Disruption of NORAD-driven PUM phase separation leads to PUM hyperactivity and genome instability that is rescued by synthetic RNAs that induce the formation of PUM condensates. These results reveal a mechanism by which RNA-driven phase separation can regulate RBP activity and identify an essential role for this process in genome maintenance. The repetitive sequence architecture of NORAD and other lncRNAs^9,10,11 suggests that phase separation may be a widely used mechanism of lncRNA-mediated regulation.

液-液相分离是亚细胞区室化^1,2的主要机制。尽管将 RNA 分离成相分离的缩合物广泛影响 RNA 代谢^3,4，但特定 RNA 是否以及如何使用相分离来调节相互作用因子，如 RNA 结合蛋白 (RBP)，以及这种调节相互作用的表型后果，是不太了解。在这里，我们表明 RNA 驱动的相分离是长链非编码 RNA (lncRNA) 控制 RBP 活性并维持哺乳动物细胞中基因组稳定性的关键机制。lncRNA NORAD通过抑制 Pumilio (PUM) 蛋白^{5,6,7,8 来}防止异常有丝分裂。我们证明了NORAD可以通过成核形成相分离的 PUM 凝聚物（称为 NP 体）来竞争数千种其他 PUM 结合转录物以抑制 PUM。PUM 募集的双重机制，涉及多价PUM- NORAD和 PUM-PUM 相互作用，使NORAD能够竞争性地隔离 NP 体内超化学计量的 PUM。NORAD驱动的PUM 相分离的破坏导致 PUM 过度活跃和基因组不稳定，这可以通过诱导 PUM 缩合物形成的合成 RNA 来挽救。这些结果揭示了 RNA 驱动的相分离可以调节 RBP 活性并确定该过程在基因组维持中的重要作用的机制。NORAD的重复序列架构和其他 lncRNA ^9,10,11表明相分离可能是一种广泛使用的 lncRNA 介导的调节机制。