The influence of capsid protein cleavage on the processing of E2 and E1 glycoproteins of rubella virus.

The structural polyprotein of rubella virus is cotranslationally processed by host cell signal peptidase. Oligonucleotide-directed mutagenesis was used to alter the cleavage site between capsid and E2 proteins and to examine the importance of this cleavage for the transport and processing of E2 and E1 glycoproteins. The in vitro and in vivo expression of the cleavage site mutant revealed that the E2 polypeptide can cross the endoplasmic reticulum membrane without the cleavage of its signal peptide, while the transport of E2 beyond the endoplasmic reticulum requires the cleavage of E2 from capsid. We have shown that capsid protein does not appear to undergo further proteolytic processing after it is cleaved from E2 by signal peptidase. Some of the requirements for the cleavage by signal peptidase between capsid and E2 were examined by the in vitro analysis of wild-type and mutant cDNAs.