||Nucleoprotein 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. It plays an important role in enhancing the efficiency of subgenomic viral RNA transcription as well as viral replication. Coronavirus nucleoproteins are phosphoproteins, and are encoded near the 3′ end of the genome. N possesses two RNA-binding domains: an N-terminal domain with adjacent S/R-rich motif and the C-terminal 209 amino acids. N protein is invovled in coronavirus infection with many ways: the C-terminal domain (CTD) of N is important for binding the genomic RNA packaging signal leading to selective genome incorporation, the N3 domain interacts with the endodomain of M to form virions, and the serine–arginine repeat region of N (SR) interacts with the first ubiquitin-like domain of nsp3 in a critical early replication step. Moreover, it has also been demonstrated that N can oligomerize through interactions in the CTD, bind viral RNA through the N-terminal domain, unwind double-stranded nucleic acid in the manner of an RNA chaperone, and pack in a helix through the N-terminal domain, though none of these other functions has yet been demonstrated to be important for infection.