SARS-CoV-2 N protein coordinates viral particle assembly through multiple domains.

Increasing evidence suggests that mutations in the nucleocapsid (N) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may enhance viral replication by modulating the assembly process. However, the mechanisms governing the selective packaging of viral genomic RNA by the N protein, along with the assembly and budding processes, remain poorly understood. Utilizing a virus-like particles (VLPs) system, we have identified that the C-terminal domain (CTD) of the N protein is essential for its interaction with the membrane (M) protein during budding, crucial for binding and packaging genomic RNA.

PABP-driven secondary condensed phase within RSV inclusion bodies activates viral mRNAs for ribosomal recruitment.

Inclusion bodies (IBs) of respiratory syncytial virus (RSV) are formed by liquid-liquid phase separation (LLPS) and contain internal structures termed "IB-associated granules" (IBAGs), where anti-termination factor M2-1 and viral mRNAs are concentrated. However, the mechanism of IBAG formation and the physiological function of IBAGs are unclear. Here, we found that the internal structures of RSV IBs are actual M2-1-free viral messenger ribonucleoprotein (mRNP) condensates formed by secondary LLPS.