Ultrastructure and morphogenesis of human immunodeficiency virus.
The ultrastructure and morphogenesis of human immunodeficiency virus (HIV) were elucidated by observation with several techniques including immunoelectron microscopy and cryo-microscopy. The virus particle consists of an envelope, a core and matrix. The virus particles were observed extracellularly as having one of three profiles: (1) a centric or an eccentric electron-dense core, (2) rod-shaped electron-dense core, and (3) doughnut-shaped. HIV-1 particles in the hydrated state were observed by high resolution electron cryo-microscopy to be globular, and the lipid membrane was clearly resolved as a bilayer. Many projections around the circumference were seen to be knob-like. The shapes and sizes of the projections, especially head parts, were found to vary in each projection. By isolation with Nonidet P40 and glutaraldehyde, HIV-1 cores were confirmed to consist of p24 protein by immunogold labeling. When the virus enters the cell, two entry modes were found: membrane fusion and endocytosis. No structures resembling virus particles could be seen in the cytoplasm after viral entry. In HIV-1-infected cells, positive reactions by immuno-labeling suggest that HIV-1 Gag may be produced in membrane-bound structures and transported to the cell surface by cytoskeletons. Then a crescent electron-dense layer was first formed underneath the cell membrane. Finally, the virus particle was released from the cell surface. Several cell clones producing defective particles were isolated from MT-4/HIV-1 cells. Among them, doughnut-shaped or teardrop-shaped particles were seen to be produced in the extracellular space. In the doughnut-shaped particles, Gag p17 and p24 proteins faced each other against the inner electron dense ring, suggesting that the inner ring consists of a precursor Gag protein.
Department of Microbiology, Osaka Medical College, Japan.
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D015496:CD4-Positive T-Lymphocytes / Q000821:virology; D002213:Capsid / Q000648:ultrastructure; D002460:Cell Line; D003673:Defective Viruses / Q000648:ultrastructure; D015870:Gene Expression; D015683:Gene Products, gag / Q000235:genetics; D015658:HIV Infections / Q000209:etiology / Q000821:virology; D015497:HIV-1 / Q000254:growth & development / Q000472:pathogenicity / Q000648:ultrastructure*; D006801:Humans; D008561:Membrane Fusion; D008854:Microscopy, Electron; D016253:Microscopy, Immunoelectron
D015683:Gene Products, gag