| SARS CoV and SARS CoV 2 nucleocapsid (N) protein is a multifunctional phosphoprotein and core structural component of the viral ribonucleoprotein complex that orchestrates viral genome packaging, replication, and immune evasion during infection. The N protein adopts a modular organization with N and C terminal RNA binding domains separated by an intrinsically disordered linker region that mediates dimerization and oligomerization, enabling cooperative binding to the large, positive strand RNA genome and the formation of a helical ribonucleoprotein particle that is encapsidated by the membrane and envelope proteins during virion assembly. In addition to its role in RNA condensation and virion biogenesis, N protein engages multiple viral and host factors: it interacts with the genomic RNA and non structural proteins of the replication–transcription complex to facilitate efficient RNA synthesis and subgenomic mRNA production, while also binding to the cytoplasmic tail of the M protein to coordinate co localization of N RNP and envelope components at the endoplasmic reticulum–Golgi intermediate compartment. The disordered linker and C terminal domain of N further serve as hubs for host protein interactions, including components of the innate immune system, where N protein mediated sequestration or post translational modification of signaling molecules constrains type I interferon and inflammatory responses, thereby supporting viral persistence and immune escape. In SARS CoV 2 infection, abundant N protein expression correlates with high viral load and disease severity, and dysregulated N driven interference with antiviral signaling and global RNA metabolism contributes to the pathogenesis of severe respiratory disease and multiorgan involvement, so that N dependent signaling and immune modulatory activity are ultimately dysregulated in the infected host. |
Lane 1: SARS-CoV NP Protein
