M glycoproteins have three transmembrane regions. M proteins are glycosylated in the Golgi apparatus. This modifcation of the M protein is crucial for the virion to fuse into the cell and to make protein antigenic. The M protein plays a key role in regenerating virions in the cell. N protein forms a complex by binding to genomic RNA and M protein triggers the formation of interacting virions in this endoplasmic reticulum-Golgi apparatus intermediate compartement (ERGIC) with this complex.