Human immunodeficiency virus is a retrovirus that carries two copies of single stranded RNA. To reproduce, HIV enters suitable host cells, particularly CD4 T lymphocytes, and uses viral enzymes alongside the host cell's biological machinery. Its replication cycle includes binding, fusion, reverse transcription, integration, viral gene expression, assembly, and budding. Each stage contributes to the production of new viral particles.
HIV genetic replication begins when the virus attaches to receptors on a CD4 cell. The viral envelope fuses with the cell membrane, allowing viral contents to enter the cell.
Reverse transcription is a defining feature of retroviruses. During this stage, HIV produces a DNA copy of its RNA genetic material. The resulting viral DNA can enter the nucleus and become integrated into the host cell's genome. This process allows HIV genetic information to use the cell's biological systems for subsequent viral gene expression.
After HIV DNA integrates into the host cell's DNA, the infected cell's transcription machinery produces viral RNA. Some of this RNA functions as genetic material for new viral particles, while other RNA molecules provide instructions for producing viral proteins. The resulting proteins and genetic material are used during the later stages of the replication cycle.
HIV enzymes have important roles throughout genetic replication. Reverse transcriptase supports the conversion of RNA into DNA, integrase facilitates the incorporation of viral DNA into host DNA, and protease processes viral proteins during maturation. Antiretroviral medicines target different stages of the HIV life cycle, including reverse transcription, integration, and viral maturation.