Synthesis and processing of the rubella virus p110 polyprotein precursor in baculovirus-infected Spodoptera frugiperda cells

In order to study the processing of rubella virus (RV) structural proteins (capsid, protein, of 33 kDa; E2 of 42–47 kDa; and E1 of 58 kDa) in Spodoptera frugiperda (fall armyworm) cells, a 24S cDNA encoding the polyprotein precursor, p110, was inserted under the transcriptional regulation of the polyhedrin gene promoter of the Autographa californica nuclear polyhedrosis virus (AcNPV) and expressed during viral infection. By immunoblot analysis using antibodies directed against whole RV and the individual structural proteins, evidence is presented that polypeptides similar to those synthesized in RV-infected B-Vero cells are expressed in this lepidopteran insect cell line infected with the recombinant baculovirus, VL1392-RV24S. The identity of the recombinant proteins was further confirmed using human convalescent sera. By expressing the recombinant proteins in the presence and absence of tunicamycin, we have further demonstrated that the 24S transcription-translation unit of RV, is expressed and proteolytically cleaved similarly, if not identically, in Sf9 cells as compared to B-Vero cells.