Encapsidates the genome protecting it from nucleases. The encapsidated genomic RNA is termed the nucleocapsid (NC) and serves as template for transcription and replication (By similarity). Homomultimerizes to form the nucleocapsid. Binds to viral genomic RNA. N in nucleocapsid binds the P protein and thereby positions the polymerase on the template (By similarity). Belongs to the paramyxoviruses nucleocapsid family.