Human immunodeficiency virus

Human immunodeficiency virus (HIV) is a human retrovirus belonging to the lentivirus family. Lentiviruses are transmitted as single-stranded, positive-sense, enveloped RNA viruses. HIV infects vital cells in the human immune system, such as helper T cells (specifically CD4+ T cells), and macrophages.

Two types of HIV have been characterized: HIV-1 and HIV-2. HIV-1 is the virus that was initially discovered and termed both lymphadenopathy associated virus (LAV) and human T-lymphotropic virus 3 (HTLV-III). HIV-1 is more virulent and more infective than HIV-2.

HIV is roughly sphericaL with a diameter of about 120 nm, around 60 times smaller than a red blood cell. It is composed of two copies of positive-sense single-stranded RNA that encodes nine genes enclosed by a conical capsid composed of 2,000 copies of the viral protein p24.

The single-stranded RNA is tightly bound to nucleocapsid proteins, p7, and enzymes needed for the development of the virion such as reverse transcriptase, proteases, ribonuclease and integrase. A matrix composed of the viral protein p17 surrounds the capsid ensuring the integrity of the virion particle.

Figure 1.The structure of HIV.

Figure 2.The genome and transcription scheme of human immunodeficiency virus 1 (HIV-1).

Figure 3.Genes and Proteins of Human Immunodeficiency Virus.

Proviral genes are located in all three reading frames, as indicated by the overlaps. HIV-1 mRNAs fall into three classes. The first is an unspliced transcript of 9.1 kb. The second class comprises singly spliced mRNAs (average length 4.3 kb) that result from splicing from a 5′ splice site upstream of the gag gene to any one of a number of 3′ splice sites near the center of the genome.

One of these mRNAs specifies the Env polyprotein precursor; others specify the accessory proteins. The third class comprises mRNAs (average length 1.8 kb) derived by multiple splicing from 5´ and 3´ splice sites throughout the genome. They include mRNAs that specify the regulatory proteins Tat, Rev, and Nef and are the first to accumulate after infection. Reproduced.