A model of the structural organization of rubella virions

Rubella virus contains three major structural polypeptides designated E1, E2, and C with molecular weights of 62,000, 47,000-54,000 (a complex), and 38,000, respectively, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reduced conditions. Limited-digest peptide maps confirm that each of these polypeptides is distinct and the E2 is a series of three closely related glycopolypeptides. Both E1 and E2 are glycosylated and covalently incorporate [3H]palmitic acid. Enzymatic digestion of intact virus with trypsin completely degrades both E1 and E2, while the C polypeptide remains intact. E1 has an isoelectric point of pH 6.5. E2 exhibits at least 15 different isoelectric species, which focus over the pH range of 5.0-8.6, and C has two distinct isoelectric species of pH 8.8 and pH 9.5. Under unreduced conditions, E1 exists as a disulfide-bonded dimer (E1-E1) with a molecular weight of 105,000; a disulfide-bounded heterodimer (E1-E2) with a molecular weight of 95,000; and in monomeric form (E1). E2 is found predominantly in heterodimeric form (E1-E2), and C is found only in dimeric form when unreduced. Functional-inhibition studies with selected monoclonal antibodies show at least three distinct antigenic domains on E1 that include sites involved in hemagglutination and lysis of red blood cells.