Forms the helical nucleocapsid (NC) in a ratio of 1 N per 6 ribonucleotides, protecting the genome from nucleases. The nucleocapsid (NC) has a helical structure with either 12.35 or 11.64 N per turn, approximately 20 nm in diameter, with a hollow central cavity approximately 5 nm in diameter. The encapsidated genomic RNA serves as template for transcription and replication; encapsidation by N is coupled to RNA synthesis. Forms the encapsidation complex with the phosphoprotein protein P. Before encapsidation, the newly synthesized free N protein, so-called N0, is chaperoned by P. Participates, together with P, in the formation of viral factories (viroplasms), which are large inclusions in the host cytoplasm where replication takes place. N is released in the blood following lysis of measles infected cells, it interacts then with human FCGR2B on immune cells, inducing apoptosis and blocking inflammatory immune response 