biostudies-literatureFang XDNational Natural Science Foundation of ChinaChina Postdoctoral Science Foundatione74884https://www.ebi.ac.uk/biostudies/studies/S-EPMC8887900biostudies-literatureUnknown11Liquid-liquid phase separation (LLPS) plays important roles in forming cellular membraneless organelles. However, how host factors regulate LLPS of viral proteins during negative-sense RNA (NSR) virus infection is largely unknown. Here, we used barley yellow striate mosaic virus (BYSMV) as a model to demonstrate regulation of host casein kinase 1 (CK1) in phase separation and infection of NSR viruses. We first found that the BYSMV phosphoprotein (P) formed spherical granules with liquid properties and recruited viral nucleotide (N) and polymerase (L) proteins in vivo. Moreover, the P-formed granules were tethered to the ER/actin network for trafficking and fusion. BYSMV P alone formed droplets and incorporated the N protein and the 5' trailer of genomic RNA in vitro. Interestingly, phase seLifeHost casein kinase 1-mediated phosphorylation modulates phase separation of a rhabdovirus phosphoprotein and virus infection.PMC88879002021T1407133210215031872920Gao QGao DMLi DWang XBZang YQiao JHXu WYWang YFang XDfalseHost casein kinase 1-mediated phosphorylation modulates phase separation of a rhabdovirus phosphoprotein and virus infection.Liquid-liquid phase separation (LLPS) plays important roles in forming cellular membraneless organelles. However, how host factors regulate LLPS of viral proteins during negative-sense RNA (NSR) virus infection is largely unknown. Here, we used barley yellow striate mosaic virus (BYSMV) as a model to demonstrate regulation of host casein kinase 1 (CK1) in phase separation and infection of NSR viruses. We first found that the BYSMV phosphoprotein (P) formed spherical granules with liquid properties and recruited viral nucleotide (N) and polymerase (L) proteins in vivo. Moreover, the P-formed granules were tethered to the ER/actin network for trafficking and fusion. BYSMV P alone formed droplets and incorporated the N protein and the 5' trailer of genomic RNA in vitro. Interestingly, phase s2022-01-01T00:00:00Z2022 Feb2025-04-04T08:41:02.25Z2025-04-04T08:41:02.25ZS-EPMC88879003519183310.7554/eLife.74884