INTRACELLULAR RETENTION OF DUCK HEPATITIS-B VIRUS LARGE SURFACE PROTEIN IS INDEPENDENT OF PRES TOPOLOGY

The mechanism of intracellular retention for the large surface protein (L) of duck hepatitis a virus (DHBV) was analyzed by examination of t he transmembrane topologies and secretory properties of a collection o f DHBV L mutants and compared with that of human hepatitis B virus (HB V) L. our results demonstrate that, in contrast to its HBV counterpart , intracellular retention of DHBV L does not depend on the cytosolic d isposition of it's preS domain: L mutants with either cytosolic or lum enal preS were mostly retained in the absence of the small surface pro tein (S), whereas coexpression with S resulted in efficient secretion of both topological forms. Coexpression of the wild-type DHBV L with S resulted in efficient incorporation of L into secreted S+L particles, whereas HBV L was partially excluded from secreted particles under th e same conditions. We propose that HBV provides L retention even in th e presence of an excess of S, by exclusion of molecules with cytosolic preS domains from secreted particles at the stage of their assembly. DHBV lacks such a retention mechanism due to the absence of topologica l selection in particulate assembly. (C) 1998 Academic Press.