Nucleocapsid protein is a most abundant protein of coronavirus. Nucleocapsid protein is a highly immunogenic phosphoprotein also implicated in viral genome replication and in modulating cell signaling pathways. While screening for ADP-ribosylated proteins during coronavirus (CoV) infection, we identified as the viral nucleocapsid (N) protein. Novel post-translation modification of the CoV N protein that may play a regulatory role for this important structural protein. The array of diverse functional activities accommodated in the hantaviral N protein goes far beyond to be a static structural protein and makes it an interesting target in the development of antiviral therapeutics. Because of the conservation of N protein sequence and its strong immunogenicity, the N protein of coronavirus is chosen as a diagnostic tool.