Background Information

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 G and M, 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 IgG N antibodies in the serum sample.