The synthesis and maturation of a non-structural extracellular antigen from tick-borne encephalitis virus and its relationship to the intracellular NS1 protein.

The replication of flaviviruses results in the secretion of four virus-coded proteins into the extracellular environment. Three of these proteins, E, C and M (or pre-M), are found in purified virions. A fourth virus-specified extracellular protein which was not present in either the slowly sedimenting haemagglutinin particles or in virions is described. The relationship of this protein to the intracellular NS1 polypeptide was investigated along with its similarity to the soluble complement-fixing antigen (SCF) reported for mosquito-borne flaviviruses. The difference in the Mr of NS1 and SCF is the result of additional glycosylation of SCF, mostly by the addition of fucose molecules. The synthesis of E and NS1 is sequential but their secretion is simultaneous, suggesting a role for NS1 in virion protein transport or virion release.