This work examines the role of human cytomegalovirus (HCMV) envelope glycoproteins in viral entry. Using genetic and biochemical approaches, we show that gO acts as a molecular chaperone for gH/gL ER export but dissociates before virion assembly; deletion of gO reduces gH/gL incorporation and blocks entry into fibroblasts and epithelial/endothelial cells. We also demonstrate that gB functions as the fusion protein: cells expressing gB mediate entry of gB-deficient virions in trans, whereas gH/gL cannot. These findings support a model where gH/gL binds cellular receptors and interacts with gB to trigger membrane fusion during HCMV entry.
