Three genes code for rubella virus structural proteins E1, E2a, E2b and C.

The structural proteins E1, E2a, E2b and C of rubella virus (RV) were purified by preparative SDS-PAGE. The individual proteins were subjected to amino-terminal sequence analysis by Edman degradation, carboxyl-terminal structure analysis by digestion with carboxypeptidases and quantitative amino acid composition analysis. The partial amino-terminal sequences of E2a and E2b were identical and different from that of E1. The C protein did not yield any consistent results on Edman degradation, suggesting that its amino-terminus is blocked. The amino acid compositions of E2a and E2b were very similar and differed from that obtained for E1 and C, which also differed from each other. Carboxypeptidase digestions showed that E2a and E2b have an identical carboxyl-terminal structure, which differed from that of the C protein. No amino acid residues were released from the E1 protein by digestion with a mixture of carboxypeptidases A and B. These results confirm that the structural proteins of RV are translated from three genes corresponding to C, E2 and E1. E2 exists in virions in two post-translationally modified forms, E2a and E2b, which have an identical apoprotein moiety. The partial amino acid sequence information obtained here should also be sufficient to localize the ends of the individual genes on the 24S mRNA genome once its nucleotide sequence has been established.