HIV belongs to a class of retroviruses that function by injecting the viral RNA into the host that express CD4; primarily CD4 T cells, dendritic cells, and macrophages (Gessani et al., 1997). The RNA is transcribed into DNA, and the viral DNA is inserted into a cellular chromosome of the host (Campbell,1996). The RNA transcripts produced from the viral DNA function as mRNA to control the synthesis of new viruses and as the RNA genome carried by the virions (Janeway et al.,1999) Specifically, HIV belongs to a class of retroviruses known as lentiviruses, which are characterized by a long period of persistence and replication before any onset of disease.

The viral envelope of HIV is composed of two layers of fatty molecules that are taken from an infected cell when the new virus buds off. Underneath the fatty molecules is a layer of matrix protein called p17. The HIV virion contains two important envelope proteins. Gp160 is a glycoprotein that is cleaved into gp120 and gp41, which are expressed as trimers to make up the viral envelope (Janeway et al. 1999). The gp120 moiety binds the virion and host via a CD4 receptor, whereas, gp41 is believed to induce fusion of the virus to the host cell membrane as well as anchor gp120 (Felser et al. 1988). On average 72 copies of the protein Env, containing three to four gp120 and three to four gp41 molecules, exist on the virus surface (Gelderblom et al., 1987 and Chan et al., 1998). The viral core of HIV is contained by 2000 copies of the viral protein, p24 (www.aegis.com). This capsid holds 2 single strands of HIV RNA that encode for the virus' nine genes (see table below). HIV RNA contains long terminal repeats (LTR) which control the synthesis of new HIV viruses when activated by the host cell or HIV (Gelderblom et al., 1987).

Gene

Gene Product

gag (group-specific antigen)

Core proteins and matrix proteins

pol (polymerase)

reverse transcriptase, protease, and integrase enzymes

env (envelope)

transmembrane glycoproteins: gp120 binds to CD4 and
CCR5; gp41 is required for virus internalization

tat (transactivator)

positive regulator of transcription

rev (regulation of viral expression)

allows export of unspliced transcripts from nucleus

vif (viral infectivity)

affects particle infectivity

vpr (viral protein R)

transport of DNA to nucleus, augments virion production,
and controls cell cycle arrest

vpu (viral protein U)

unique to HIV-1; downregulates CD4

nef (negative-regulation factor)

augments viral replication in vivo and in vitro; downregulates
CD4