Packages the positive strand viral genome RNA into a helical ribonucleocapsid (RNP) and plays a fundamental role during virion assembly through its interactions with the viral genome and membrane protein M. Plays an important role in enhancing the efficiency of subgenomic viral RNA transcription as well as viral replication (By similarity). May induce inflammasome responses in cultured cells and mice. Acts by interacting with host NLRP3 to facilitate inflammasome assembly, which induces cytokine release that may play a role in COVID lung injury. Homooligomer. Both monomeric and oligomeric forms interact with RNA. Interacts with protein M. Interacts with protein E. Interacts with NSP3; this interaction serves to tether the genome to the newly translated replicase-transcriptase complex at a very early stage of infection (By similarity). May interact with host NLRP3 (PubMed:34341353). Located inside the virion, complexed with the viral RNA. Probably associates with ER-derived membranes where it participates in viral RNA synthesis and virus budding. ADP-ribosylated. The ADP-ribosylation is retained in the virion during infection. Phosphorylated on serine and threonine residues. Variant Alpha/B.1.1.7 belongs to a lineage isolated first in United Kingdom (December 2020). It is also called Variant of Concern (VOC) 202012/01, Variant Under Investigation (VUI) 202012/01, 501Y.V1 or 20B/501Y.V1. Variant Omicron/BA.1 and BA.2 belong to a lineage first isolated in South Africa (November 2021). Belongs to the betacoronavirus nucleocapsid protein family.