Herpes simplex virus type 1 entry into host cells: Reconstitution of capsid binding and uncoating at the nuclear pore complex in vitro

During entry, herpes simplex virus type 1 (HSV-1) releases its capsid and t he tegument proteins into the cytosol of a host cell by fusing with the pla sma membrane. The capsid is then transported to the nucleus, where it docks at the nuclear pore complexes (NPCs), and the viral genome is rapidly rele ased into the nucleoplasm. In this study, capsid association with NPCs and uncoating of the viral DNA were reconstituted in vitro. Isolated capsids pr epared from virus were incubated with cytosol and purified nuclei. They wer e found to bind to the nuclear pores. Binding could be inhibited by pretrea ting the nuclei with wheat germ agglutinin, anti-NPC antibodies, or antibod ies against importin beta. Furthermore, in the absence of cytosol, purified importin beta was both sufficient and necessary to support efficient capsi d binding to nuclei. Up to 60 to 70% of capsids interacting with rat liver nuclei in vitro released their DNA if cytosol and metabolic energy were sup plied. Interaction of the capsid with the nuclear pore thus seemed to trigg er the release of the viral genome, implying that components of the NPC pla y an active role in the nuclear events during HSV-1 entry into host cells.