The HIV Replication Cycle
HIV Replication
This educational module takes you step-by-step through the process by which a healthy cell, normally a T-cell (white blood cell) becomes infected by an HIV virion (virus particle) and then produces many new virions.
Click any of the 7 stages to learn more.
1. Entry
Proteins, called envelope proteins, embedded in the outer membrane of the HIV virion bind to receptors on the surface of target cells. T-cells (white blood cells) have CD4 and CCR5 receptors to which HIV can bind. Binding of the HIV envelope protein to CD4 and CCR5 allows the HIV-1 outer membrane to fuse with the cell’s outer membrane and the contents of the virus particle to enter the cell.
2. Reverse Transcription
The genetic material of the virus is in the form of RNA, or ribonucleic acid. There are two strands of RNA in each HIV-1 virus particle. An enzyme known as reverse transcriptase initiates the formation of one double-stranded molecule of viral DNA (deoxyribonucleic acid) by copying the sequence of the RNA strands contained in the virus particle.
3. Integration
The viral DNA enters the nucleus of the host and becomes integrated into the host’s DNA. An enzyme called integrase is key in this process. Once the viral DNA has integrated into the cell’s DNA, the cell is infected for the remainder of its life. The integrated viral DNA is now referred to as a provirus.
4. Transcription
The provirus DNA serves as a template for the creation of new viral RNA via a process known as transcription. The host cell’s own machinery that is normally used for the transcription of human genes is used by the virus to create new viral RNA molecules. The newly formed viral RNA moves out of the infected cell’s nucleus.
5. Translation
The viral RNA carries code for the synthesis of viral proteins and enzymes. The code is translated into long chains of amino-acids, known as a polypeptide chains, which fold to form the protein and enzyme components of new virus particles.
6. Assembly
Components that are required to build new virus particles, namely viral proteins, enzymes and genetic material (viral RNA) move to the cell’s outer membrane where they accumulate and assemble in the form of a bud. A variety of host cell proteins are recruited to assist in virus assembly.
7. Release and Maturation
Host-cell proteins cut the virus bud from the cell’s outer membrane, thereby releasing a new virus particle. During and after assembly and release, a viral enzyme called protease cuts the HIV polypeptide chains at several positions, in a process called maturation, to make the finished components of the new, infectious, virus particle. A single infected cell can release many new HIV particles which move on to infect other cells in various parts of the body, where the viral life cycle is repeated. The infected cells are eventually destroyed.
