The gene order for rubella virus structural proteins is NH2-C-E2-E1-COOH

Abstract

The order of translation in vivo of the genes coding for rubella virus structural proteins was studied in infected B-Vero cells. The proteins were sequentially pulse-chase labeled with [35S]methionine after synchronization of translation initiation with hypertonic salt treatment. A sequential labeling procedure ("window-labeling") to specifically label defined segments of the structural proteins was also used. The labeled proteins were identified by sodium dodecyl sulfate-gel electrophoresis after immunoprecipitation with specific antisera directed against the two virion glycoproteins (E1 and E2a/E2b) and the nucleocapsid (C) protein. The order of translation was found to be NH2-C-E2-E1-COOH. We have previously shown that the structural proteins are synthesized in vitro from a cytoplasmic 24S subgenomic mRNA as a 110,000-dalton (p110) precursor (Oker-Blom et al., J. Virol. 49:403-408, 1984). Here, it is shown that p110 is precipitated with anti-C, anti-E2, and anti-E1 sera, indicating that p110 is the precursor of all three structural proteins. Two major in vitro translation products (Mrs, 66,000 and 62,000) that could represent preterminated polypeptide chains or proteolytic cleavage products were precipitated with anti-C and anti-E2 sera, but not with anti-E1 serum, indicating, in conformity with the in vivo results, that the genes for the C and E2 proteins are adjacent to each other. Using these specific antisera, we have also confirmed the identity of the unglycosylated forms of E1 (Mr, 53,000) and E2 (Mr, 30,000) immunoprecipitated from tunicamycin-treated infected cells.