Characterization of novel viral polyproteins detected in cells infected by the flavivirus Kunjin and radiolabelled in the presence of the leucine analogue hydroxyleucine.

Vero cells were infected by Kunjin virus and radiolabelled in the presence of the leucine analogue, threo-beta-hydroxy-DL-leucine (THL). This analogue is known to prevent preprotein processing in cell-free systems when incorporated into signal peptides. Novel Kunjin virus-specified proteins were detected, namely gp140, p120 and gp92; the designations for the proteins indicate their approximate Mr X 10(-3) and whether they are glycosylated. The glycoproteins gp140 and gp92 were observed in cells labelled with [3H]mannose and bound to concanavalin A. Limited proteolytic digestion of gp140, gp92 and gp66 (related to the envelope protein E), and tryptic peptide mapping of these three glycoproteins and p120 indicated that all four were closely related. The glycoproteins gp140 and gp92 were also detected in cells infected by West Nile virus radiolabelled in the presence of THL. Other effects of THL in Kunjin virus-infected cells were a reduction in the incorporation of radioactive amino acids or mannose, a decrease in the yield of haemagglutinin and infectious virus, an inhibition of processing of gp66 to gp53 and an apparent inhibition of synthesis of P98 and P71. We suggest possible explanations for the THL-induced changes in infected cells based on recent models proposed for the synthesis of the yellow fever and West Nile viral proteins.