MEMBRANE ANCHORING DOMAIN OF HERPES-SIMPLEX VIRUS GLYCOPROTEIN GB IS SUFFICIENT FOR NUCLEAR-ENVELOPE LOCALIZATION

We have used the glycoprotein gB of herpes simplex virus type 1 (gB-1) , which buds from the inner nuclear membrane, as a model protein to st udy localization of membrane proteins in the nuclear envelope. To dete rmine whether specific domains of gB-1 glycoprotein are involved in lo calization in the nuclear envelope, we have used deletion mutants of g B-1 protein as well as chimeric proteins constructed by replacing the domains of the cell surface glycoprotein G of vesicular stomatitis vir us with the corresponding domains of gB. Mutant and chimeric proteins expressed in COS cells were localized by immunoelectron microscopy. A chimeric protein (gB-G) containing the ectodomain of gB and the transm embrane and cytoplasmic domains of G did not localize in the nuclear e nvelope. When the ectodomain of G was fused to the transmembrane and c ytoplasmic domains of gB, however, the resulting chimeric protein (G-g B) was localized in the nuclear envelope. Substitution of the transmem brane domain of G with the 69 hydrophobic amino acids containing the m embrane anchoring domain of gB allowed the hybrid protein (G-tmgB) to be localized in the nuclear envelope, suggesting that residues 721 to 795 of gB can promote retention of proteins in the nuclear envelope. D eletion mutations in the hydrophobic region further showed that a tran smembrane segment of 21 hydrophobic amino acids, residues 774 to 795 o f gB, was sufficient for localization in the nuclear envelope. Since w ild-type gB and the mutant and chimeric proteins that were localized i n the nuclear envelope were also retained in the endoplasmic reticulum , the membrane spanning segment of gB could also influence retention i n the endoplasmic reticulum.