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The genome and proteins of HIV (human immunodeficiency virus) have been the subject of extensive research since the discovery of the virus in 1983. Each virion comprises a viral envelope and associated matrix enclosing a capsid, which itself encloses two copies of the single-stranded RNA genome and several enzymes. The discovery of the virus itself did not occur until two years after the first major cases of AIDS associated illnesses were reported in 1981. ==Structure== HIV is different in structure from other retroviruses. It is around 120 nm in diameter (around 60 times smaller than a red blood cell) and roughly spherical. HIV-1 is composed of two copies of noncovalently linked, unspliced, positive-sense single-stranded RNA enclosed by a conical capsid composed of the viral protein p24, typical of lentiviruses.〔Montagnier, Luc. (1999) Human Immunodeficiency Viruses (Retroviridae). Encyclopedia of Virology (2nd Ed.) 763-774〕〔 〕 The RNA component is 9749 nucleotides long and bears a 5’ cap (Gppp), a 3’ poly(A) tail, and many open reading frames (ORFs).〔Castelli, Joann C. and Levy, Jay A. (2002) HIV (Human Immunodeficiency Virus). Encyclopedia of Cancer (2nd Ed.) 2:407--415〕 Viral structural proteins are encoded by long ORFs, whereas smaller ORFs encode regulators of the viral life cycle: attachment, membrane fusion, replication, and assembly.〔 The single-strand RNA is tightly bound to p7 nucleocapsid proteins, late assembly protein p6, and enzymes essential to the development of the virion, such as reverse transcriptase and integrase. Lysine tRNA is the primer of the magnesium-dependent reverse transcriptase.〔 The nucleocapsid associates with the genomic RNA (one molecule per hexamer) and protects the RNA from digestion by nucleases. Also enclosed within the virion particle are Vif, Vpr, Nef, and viral protease. A matrix composed of an association of the viral protein p17 surrounds the capsid, ensuring the integrity of the virion particle. This is in turn surrounded by an envelope of host-cell origin. The envelope is formed when the capsid buds from the host cell, taking some of the host-cell membrane with it. The envelope includes the glycoproteins gp120 and gp41. As a result of its role in virus-cell attachment, the structure of the virus envelope spike, consisting of gp120 and gp41, is of particular importance. Determining the envelope spike's structure will contribute to understanding the HIV replication cycle, and may help in the creation of a cure. The first model of its structure was compiled in 2006 using cryo-electron tomography and suggested that each spike consists of a trimer of three gp120–gp41 heterodimers. However, published shortly after was evidence for a single-stalk "mushroom" model, with a head consisting of a trimer gp120s and a gp41 stem, which appears as a compact structure with no obvious separation between the three monomers, anchoring it to the envelope. There are various possibilities as to the source of this difference, as it is unlikely that the viruses imaged by the two groups were structurally different. More recently, further evidence backing up the heterodimer trimer-based model has been found. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Structure and genome of HIV」の詳細全文を読む スポンサード リンク
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