Structure and genomic organization of human immunodeficiency virus
المؤلف:
Baijayantimala Mishra
المصدر:
Textbook of Medical Virology
الجزء والصفحة:
2nd Edition , p250-251
2025-12-02
17
HIVs are enveloped single-stranded, positive sense RNA viruses, with icosahedral symmetry. Mature viral particles measure approximately 100 to 150 nm in diameter. The core contains two copies of single-stranded RNA, approximately 10 kb in length, which are surrounded by structural proteins that form the nucleocapsid and the matrix and by products of the pol gene. The outer envelop contains several glycoprotein complexes. Each of this glycoprotein complex is a trimmer of two components; outer gp120 and a trnasmembrane component gp41. These surface glycoproteins mediate the binding of virus to CD4 and other co-receptors. Besides the viral glycoprotein, envelop may also contain certain host cell proteins, such as HLA class-I, HLA class-II and intercellular adhesion molecule-1 (ICAM-1). These host cell proteins get incorporated during the process of budding and may play a role in binding to other target cells. Below the envelop, the p17 matrix protein is present, which covers the capsid that consists of p24 proteins. The two copies of viral RNA genome are located at the innermost part of the virus particle which lies inside the capsid. Several enzymes that are required for viral replication are entangled to viral RNA in a complex form, of which reverse transcriptase and integrase are most important (Fig. 1).
Fig1. Schematic diagram of HIV-1 structure
The viral genome primarily comprises three genes (gag, pol, env) that encodes for the structural proteins and six other genes (tat, rev, nef, vif, vpr, and vpu) that code for various regulatory proteins which play a significant role in virus pathogenesis.
The gag gene (group antigen) encodes for nucleocapsid, capsid and matrix proteins including p24; pol or polymerase gene encodes for reverse transcriptase as well as protease, RNAse and integrase and env or envelop gene encodes for the envelop glycoproteins. These three genes in the sequence of gag-pol-env are flanked on both sides by long terminal repeats (LTR) which are present on both ends of the viral gnome.
HIV-2 differs structurally from HIV-1 in having a vpx gene in place of vpu gene and also the outer envelop and transmembrane glycoproteins are gp125 and gp36, and the core proteins are p16 and p26 instead of p17 and p24 in HIV-1.
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