Coronavirus nucleocapsid protein

The nucleocapsid (N) protein is a protein that packages the positive-sense RNA genome of coronaviruses to form ribonucleoprotein structures enclosed within the viral capsid. The N protein is the most highly expressed of the four major coronavirus structural proteins. In addition to its interactions with RNA, N forms protein-protein interactions with the coronavirus membrane protein (M) during the process of viral assembly. N also has additional functions in manipulating the cell cycle of the host cell. The N protein is highly immunogenic and antibodies to N are found in patients recovered from SARS and COVID-19. COVID-19 was first identified in January 2020. A patient in the state of Washington was given a diagnosis of coronavirus infection on 20 January. A group of scientists based at the Centers for Disease Control and Prevention in Atlanta, Georgia isolated the virus from nasopharyngeal and oropharyngeal swabs and were able to characterize the genomic sequence, replication properties and cell culture tropism from the swabs. They made available the virus to the wider scientific community shortly thereafter "by depositing it into two virus reagent repositories". The N protein is composed of two main protein domains connected by an intrinsically disordered region (IDR) known as the linker region, with additional disordered segments at each terminus. A third small domain at the C-terminal tail appears to have an ordered alpha helical secondary structure and may be involved in the formation of higher-order oligomeric assemblies. In SARS-CoV, the causative agent of SARS, the N protein is 422 amino acid residues long and in SARS-CoV-2, the causative agent of COVID-19, it is 419 residues long. Both the N-terminal and C-terminal domains are capable of binding RNA. The C-terminal domain forms a dimer that is likely to be the native functional state. Parts of the IDR, particularly a conserved sequence motif rich in serine and arginine residues (the SR-rich region), may also be implicated in dimer formation, though reports on this vary.