Human immunodeficiency virus (HIV), or AIDS (acquired immunodeficiency syndrome), is a virus that causes defects in the human immune system. HIV was first discovered in the United States in 1981. HIV infect human which leads to paralysis of the immune system by destructing T lymphocytes, and then blocks processes of the cellular immune and humoral immune, eventually leads to AIDS. So far as, there is no efficient vaccine to prevent this virus from humans, since the mutation rate of HIV is extremely high, and thus has become a great threat to human health. Recently, there are four HIV strains, named M, N, O and P type, all come from Cameroon chimpanzees and gorillas. Each of these four species has unique source, and we now know that the most widely spread of M and N have been confirmed from chimpanzees, while the rare O and P types have been confirmed from gorillas of southwestern Cameroon.
The diameter of HIV particle consists of about 120 nm, roughly spherical. The outer membrane of HIV is a lipid envelope, which comes from the host cell, is embedded with the viral proteins gp120 and gp41; gp41 is a transmembrane glycoprotein, gp120 locates on the viral surface, and binds to gp41 through noncovalent interactions. Matrix consists of protein p17, and a half-tapered capsid (Capsid) formed by protein p24, which shows a high electron density under electron microscopy. The capsid contains the RNA genome of the virus, enzymes (reverse transcriptase, integrase and protease) and other components from the host cell (such as tRNAlys3, as a reverse transcription primer). Figure 1 shows the schematic model of HIV particle:
Fig. 1 the Schematic Model of Human Immunodeficiency Virus
The viral genome has two identical positive-strand RNAs, each containing about 9.2-9.8 kb. Long terminal repeats (LTR) of both ends contain the cis-regulatory sequences and control the expression of the pre-virus. Promoters and enhancers have been shown to have a negative regulatory region in the LTRs. The sequences between LTRs encode at least nine proteins, which can be divided into three classes: structural proteins, regulatory proteins, and accessory proteins.