FLAVIVIRUS PREMEMBRANE PROTEIN CLEAVAGE AND SPIKE HETERODIMER SECRETION REQUIRE THE FUNCTION OF THE VIRAL PROTEINASE NS3

Flavivirus protein biosynthesis involves the proteolytic processing of a single polyprotein precursor by host- and virus-encoded proteinases . In this study, the requirement for the proteolytic function of the v iral proteinase NS3 for correct processing of a polyprotein segment en compassing the Murray Valley encephalitis virus structural proteins is shown. The NS3-mediated cleavage in the structural polyprotein region presumably releases the capsid protein from its membrane anchor and t riggers the appearance of the premembrane (prM) protein. This suggests that cleavage of prM by signal peptidase in the lumen of the endoplas mic reticulum is under control of a cytoplasmic cleavage catalyzed by a viral proteinase. The function of the viral proteinase is also essen tial for secretion of flaviviral spike proteins when expressed from cD NA via vaccinia virus recombinants or in COS cell transfections. This has important implications for the design of flavivirus subunit vaccin es.