Plays a major role in assembly and budding of virion. Condensates the ribonucleocapsid core during virus assembly. Shut off cellular transcription by inhibiting mRNA nuclear export through direct interaction with host RAE1-NUP98 complex. This shutoff presumably inhibit interferon signaling and thus establishment of antiviral state in virus infected cells. Induces cell-rounding, cytoskeleton disorganization and apoptosis in infected cell (By similarity). Homomultimer. Interacts with viral nucleocapsid (By similarity). Late-budding domains (L domains) are short sequence motifs essential for viral particle budding. They recruit proteins of the host ESCRT machinery (Endosomal Sorting Complex Required for Transport) or ESCRT-associated proteins. M contains two overlapping L domains: a PPXY motif which interacts with the WW domain 3 of NEDD4 and a PTAP/PSAP motif, which interacts with the UEV domain of TSG101 (By similarity). Phosphorylated by host. Most abundant protein in the virion. Belongs to the vesiculoviruses matrix protein family.