EFFECTS OF DELETIONS IN THE CARBOXY-TERMINAL HYDROPHOBIC REGION OF HERPES-SIMPLEX VIRUS GLYCOPROTEIN-GB ON INTRACELLULAR-TRANSPORT AND MEMBRANE ANCHORING

The gB glycoprotein of herpes simplex virus type 1 is involved in vira l entry and fusion and contains a predicted membrane-anchoring sequenc e of 69 hydrophobic amino acids, which can span the membrane three tim es, near the carboxy terminus. To define the membrane-anchoring sequen ce and the role of this hydrophobic stretch, we have constructed delet ion mutants of gB-1, lacking one, two, or three predicted membrane-spa nning segments within the 69 amino acids. Expression of the wild-type and mutant glycoproteins in COS-1 cells show that the mutant glycoprot eins lacking segment 3 (amino acids 774 to 795 of the gB-1 protein) we re secreted from the cells. Protease digestion and alkaline extraction of microsomes containing labeled mutant proteins further showed that segment 3 was sufficient for stable membrane anchoring of the glycopro teins, indicating that this segment may specify the transmembrane doma in of the gB glycoprotein. Also, the mutant glycoproteins containing s egment 3 were localized in the nuclear envelope, which is the site of virus budding. Deletion of any of the hydrophobic segments, however, a ffected the intracellular transport and processing of the mutant glyco proteins. The mutant glycoproteins, although localized in the nuclear envelope, failed to complement the gB-null virus (K082). These results suggest that the carboxy-terminal hydrophobic region contains essenti al structural determinants of the functional gB glycoprotein.