Encapsidates the genome in a ratio of 1 N per 6 ribonucleotides, protecting it 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 is termed the NC and serves as template for transcription and replication. During replication, encapsidation by N is coupled to RNA synthesis and all replicative products are resistant to nucleases. 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. Ntail binds to a protein on human thymic epithelial cells, termed Nucleoprotein Receptor (NR), inducing growth arrest (By similarity). Homomultimerizes to form the nucleocapsid. Binds to viral genomic RNA. In nucleocapsid, binds the P protein and thereby positions the polymerase on the template. Interacts with human FCGR2B protein (By similarity). Interacts with human PPIA/CYPA and PPIB/CYPB (PubMed:20147391). Ncore is globular and carries regions required for N self-assembly and RNA-binding. Ntail is an intrinsically disordered monomeric domain (By similarity). Belongs to the paramyxoviruses nucleocapsid family.