HIV life-cycle. Computer illustration describing the replication cycle of HIV (human immunodeficiency virus). The cycle begins when an HIV virion (particle) fuses with the surface of the host cell. A capsid containing the virus's genome and proteins then enters the cell. The shell of the capsid disintegrates and the HIV protein called reverse transcriptase transcribes the viral RNA (ribonucleic acid) into DNA (deoxyribonucleic acid). The viral DNA is transported across the nucleus, where the HIV protein integrase integrates the HIV DNA into the host's DNA. The host's normal transcription machinery transcribes HIV DNA into multiple copies of new HIV RNA. Some of this RNA becomes the genome of a new virus, while the cell uses other copies of the RNA to make new HIV proteins. The new viral RNA and HIV proteins move to the surface of the cell, where a new, immature HIV virion forms. Finally, the virion is released from the cell, and the HIV protein called protease cleaves newly