Plays a crucial role in virion assembly and budding. Homooligomer (PubMed:15862310). Forms homotetramers (By similarity). Interacts with phosphoprotein P (PubMed:17079312). Binds to ssRNA (By similarity). During viral budding, associates with the inner side of the plasma membrane of infected cells (By similarity). Found in nuclear punctate structures that have been proposed to be the sites of viral replication and transcription, also termed viral speckles of transcripts (vSPOTs).