Human immunodeficiency virus (HIV) belongs to the Family Retroviridae, RNA retroviruses that use the enzyme reverse transcriptase to convert viral RNA into DNA. It consists of two primary components: a core of ribonucleic acid (RNA), called the genome, and a protein component that surrounds the genome, called a capsid.
- The genome carries the genetic information of the virus, while the capsid gives the virus its shape and protects the genome.
- The HIV genome consists of three major genes: group-specific antigens (Ags) or capsid proteins (gag); polymerase gene proteins: reverse transcriptase, protease, and integrase enzymes (pol); and envelope glycoproteins (env).
- The capsid is made up of subunits called capsomeres.
Viral proteins are identified as either "gp" for glycoprotein or "p" for protein, followed by the molecular weight in kilodaltons. For example, HIV-1 includes the envelope proteins gp160, gp120, and gp41; the gag core gene proteins, p55, p24, and p17; the polymerase gene proteins, p66, p51, and p31.
HIV-2 proteins are similar to HIV-1 proteins; however, some proteins differ in molecular weight from those found in HIV-1. For example, the gag core gene proteins in HIV-2 are p56, p26, and p16.