Translocation and cleavage of rubella virus envelope glycoproteins: identification and role of the E2 signal sequence

The structural proteins of rubella virus (RV) are translated as a large polyprotein precursor, p l l0, which is processed to produce the mature virion components, the 33K capsid protein (C) and the two envelope glycoproteins, E1 (58K) and E2 (42K to 47K). The precise processing mechanism has not been elucidated; however it must include at least two proteolytic leavages to release the individual virion components from the polyprotein, and it must provide for their dichotomous intracellular distribution. The C protein remains in the cytoplasm where it participates in the formation of nucleocapsids, while the envelope glycoproteins enter the cellular secretory pathway and are N-glycosylated and cleaved. Sequence analysis of the 24S mRNA encoding the polyprotein precurso