GP is synthesized as a single polypeptide. In the late Golgi, GP is cleaved by a furin-like protease in two subunits; a surface subunit GP1 and a transmembrane subunit GP2. GP1 is linked with GP2 through a disulfide bond. GP on the surface of virions is present as a trimer. The GP1 subunit is involved in receptor binding and the GP2 subunit is involved in fusion of the viral and host membranes.