Translocation of rubella virus glycoprotein E1 into the endoplasmic reticulum

Rubella virus (RV) contains four structural proteins, C (capsid), E2a, E2b, and E1, which are derived from posttranslational processing of a single polyprotein precursor, p110. C protein is nonglycosylated and is thought to interact with RV RNA to form a nucleocapsid. E1 and E2 are membrane glycoproteins that form the spike complexes located on the virion exterior. Two different E1 cDNAs were used to analyze the requirements for translocation of E1 into the endoplasmic reticulum. Analysis of expression of these cDNAs both in vivo and in vitro showed that RV E1 was stably expressed and glycosylated in COS cells and correctly targeted into microsomes in the absence of E2 glycoprotein. The results provide experimental evidence that translocation of RV E1 glycoprotein into the endoplasmic reticulum is mediated by a signal peptide contained within the 69 carboxyl-terminal residues of E2.