THE CYTOPLASMIC AND TRANSMEMBRANE DOMAINS OF THE VACCINIA VIRUS B5R PROTEIN TARGET A CHIMERIC HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 GLYCOPROTEIN TO THE OUTER ENVELOPE OF NASCENT VACCINIA VIRIONS

The outer envelope of the extracellular form of vaccinia virus (EEV) i s derived from the Golgi membrane and contains at least six viral prot eins. Transfection studies indicated that the EEV protein encoded by t he B5R gene associates with Golgi membranes when synthesized in the ab sence of other viral products, a domain swapping strategy was then use d to investigate the possibility that the B5R protein contains an EEV targeting signal. We constructed chimeric genes encoding the human imm unodeficiency virus (HIV) type 1 glycoprotein with the cytoplasmic and transmembrane domains replaced by the corresponding 42-amino-acid C-t erminal segment of the B5R protein. Recombinant vaccinia viruses that stably express a chimeric B5R-HIV protein or a control HIV envelope pr otein with the original cytoplasmic and transmembrane domains were iso lated. Cells infected with recombinant vaccinia viruses that expressed either the unmodified or the chimeric HIV envelope protein formed syn cytia with cells expressing the CD4 receptor for HIV. However, biochem ical and microscopic studies demonstrated that the HIV envelope protei ns with the B5R cytoplasmic and transmembrane domains were preferentia lly targeted to the EEV. These data are consistent with the presence o f EEV localization signals in the cytoplasmic and transmembrane domain s of the B5R protein.