Negative-stranded RNA viruses can establish long-term persistent infection in the form of large intracellular inclusions in the human host and cause chronic diseases. Here, we uncover how cellular stress disrupts the metastable host-virus equilibrium in persistent infection and induces viral replication in a culture model of mumps virus. Using a combination of cell biology, whole-cell proteomics, and cryo-electron tomography, we show that persistent viral replication factories are dynamic condensates and identify the largely disordered viral phosphoprotein as a driver of their assembly. Upon stress, increased phosphorylation of the phosphoprotein at its interaction interface with the viral polymerase coincides with the formation of a stable replication complex. By obtaining atomic models for the authentic mumps virus nucleocapsid, we elucidate a concomitant conformational change that exposes the viral genome to its replication machinery. These events constitute a stress-mediated switch within viral condensates that provide an environment to support upregulation of viral replication.

负链RNA病毒可以在人类宿主体内以大细胞内包涵体的形式建立长期持续感染并引起慢性疾病。在这里，我们揭示了细胞应激如何破坏持续感染中的亚稳态宿主-病毒平衡，并在腮腺炎病毒培养模型中诱导病毒复制。结合细胞生物学、全细胞蛋白质组学和冷冻电子断层扫描，我们证明了持久的病毒复制工厂是动态凝聚物，并将很大程度上无序的病毒磷蛋白识别为它们组装的驱动因素。在压力下，磷蛋白在其与病毒聚合酶的相互作用界面处的磷酸化增加与稳定复制复合物的形成一致。通过获得真正的腮腺炎病毒核衣壳的原子模型，我们阐明了伴随的构象变化，将病毒基因组暴露给其复制机制。这些事件构成了病毒凝聚物中压力介导的开关，提供了支持病毒复制上调的环境。