Rubella virus (RV), the etiological agent of German measles, is a small enveloped RNA virus that belongs to the togavirus family. RV virions contain two glycosylated membrane proteins, E1 and E2, that exist as a heterodimer and form the viral spike complexes on the virion surface. Formation of an E1-E2 heterodimer is required for transport of E1 out of the endoplasmic reticulum lumen to the Golgi apparatus and plasma membrane.