Nuclear translocation of mutagenized forms of human cytomegalovirus glycoprotein B (gpUL55)

To define structural elements involved in translocation of human cytomegalovirus (HCMV) glycoprotein B (gB) to the inner nuclear membrane (INM) compartment, mutagenized gB derivatives with deletions of the potential membrane anchor domains or of portions of the cytoplasmic tail were stably expressed in human astrocytoma cells. Subcellular localization examined by immunofluorescence and cell fractionation suggested that all gB derivatives reached the INM; however, reduced amounts were found after deletion of the extreme carboxy terminus [amino acids 856-906; gB(Del3)]. Pulse-chase analysis revealed accumulation in nuclear fractions of all gB derivatives during the chase, except for gB(Del3), which exhibited impaired nuclear retention. A carboxy-terminal nucleoplasmin-like signal localized within the respective deletion may thus be involved in nuclear transport and retention of HCMV gB. Immunoprecipitation after 32P-radiolabelling of the gB transfectants verified that the gB molecule is phosphorylated at a carboxy-terminal consensus motif for casein kinase II.