ROLE OF ENVELOPE PROTEIN GE ENDOCYTOSIS IN THE PSEUDORABIES VIRUS LIFE-CYCLE

Several groups have reported that certain herpesvirus envelope protein s do not remain on the surface of cells that express them but rather a re internalized by endocytosis in a recycling process. The biological function of membrane protein endocytosis in the virus life cycle remai ns a matter of speculation and debate. In this report, we demonstrate that some, but not all, membrane proteins encoded by the alphaherpesvi rus pseudorabies virus (PRV) are internalized after reaching the plasm a membrane. Glycoproteins gE and gB are internalized from the plasma m embrane of cells, while gI and gC are not internalized efficiently. We show for gE that the cytoplasmic domain of the protein is required fo r endocytosis. While the gI protein is incapable of endocytosis on its own, it can be internalized when complexed with gE. We demonstrate th at endocytosis of the gE-gI complex and gB occurs early after infectio n of tissue culture cells but that this process stops completely after 6 h of infection, a time that correlates with significant shutoff of host protein synthesis. We also show that gE protein internalized at 4 h postinfection is not present in virions formed at a later time. We discuss the differences in PRV gE and gI endocytosis compared to that of the varicella-zoster virus homologs and the possible roles of glyco protein endocytosis in the virus life cycle.