Coronaviruses are enveloped viruses with a positive-sense RNA genome and with a nucleocapsid
of helical symmetry. Coronavirus nucleoproteins localize to the cytoplasm and the nucleolus, a
subnuclear structure, in both virus-infected primary cells and in cells transfected with plasmids that express N protein. Coronavirus N protein is required for coronavirus RNA synthesis, and has RNA chaperone activity that may be involved in template switch. Nucleocapsid protein is a most abundant protein of coronavirus. During virion assembly, N protein binds to viral RNA and leads to formation of the helical nucleocapsid. Nucleocapsid protein is a highly immunogenic phosphoprotein also implicated in viral genome replication and in modulating cell signaling pathways . Because of the conservation of N protein sequence and its strong immunogenicity, the N protein of coronavirus is chosen as a diagnostic tool. COVID-19 antibodies can be produced by a host immune system following exposure to SARS-CoV-2. IgG and IgM antibodies are also known as immunoglobulins IgG and IgM, respectively, and are among the antibody isotypes produced by vertebrate immune systems. The ELISA microplate is coated with the SARS-CoV-2 nucleocapsid (N) protein. The coated N protein binds with COVID-19 IgM N antibodies in the serum sample.