Retroviruses & HIV

Human Immunodeficiency Virus (HIV) is a retrovirus and upon infection, results in Acquired Immune Deficiency Syndrome (AIDS).

When HIV infects a cell, it injects its RNA into the cytoplasm of that cell along with the reverse transcriptase enzyme. The cDNA produced from the RNA template contains the genetic instructions which allows infection of the host cell to proceed. In order to inject its genetic information into the host cell, the HIV must bind its envelope glycoprotein gp120 to molecules on the surface of the cell. Only cells that carry the appropriate molecules are susceptible to infection by HIV.

Scientists have found that a molecule called CD4, which is found particularly on certain T-lymphocytes was the pirmary binding site but other co-receptors have since been discovered. Fusion of the virus with the cell membrane permits the viral nucleiod to enter the cell.

The human immunodeficiency virus attaches to the CD4 protein on the surface of a T-lymphocyte, and the viral envelope fuses with the cell membrane. This fusion releases the viral nucleoid into the cell, where the reverse transcriptase enzyme converts the virion RNA into double-stranded DNA. The viral DNA enters the nucleus of the cell and is integrated into the cellular DNA. Normal cellular processes transcribe the integrated DNA into new virion RNA and viral messenger RNA, and translate the viral messenger RNA into new viral proteins. The proteins and the virion RNA are assembled into a new viral nucleoid, which buds off from the T-lymphocyte, taking a piece of the host cell’s membrane for its envelope.