Provirus

A provirus is a viral genome that is integrated into the DNA of a host cell. This integration allows the virus to replicate along with the host cell's DNA, potentially leading to long-term or persistent infection. The term is most commonly associated with retroviruses, such as HIV, but can also apply to other viruses that integrate their DNA into the host's genome.

When a retrovirus infects a cell, it uses an enzyme called reverse transcriptase to convert its RNA genome into DNA. This viral DNA then enters the host cell's nucleus and is integrated into the host's chromosomal DNA. Once integrated, the viral DNA is referred to as a provirus.

The provirus may remain latent (inactive) for an extended period, meaning that it is not actively producing new virus particles. During this latent phase, the provirus is replicated along with the host cell's DNA during cell division. Alternatively, the provirus may become activated, leading to the transcription of viral genes and the production of new virus particles.

The integration of a provirus into the host genome can have several consequences for the host cell. In some cases, the integration may disrupt the function of essential host genes, leading to cell death or transformation. In other cases, the provirus may have no apparent effect on the host cell. The ability of a provirus to integrate into the host genome and persist for long periods is a key characteristic of retroviral infections and contributes to the difficulty of eradicating these viruses from the body.

Proviruses can also be found in the germline (sperm and egg cells), leading to the transmission of viral genetic material from parent to offspring. These inherited proviruses are called endogenous retroviruses (ERVs) and make up a significant portion of the genomes of many organisms. ERVs are often inactive due to mutations accumulated over time, but in some cases, they can be reactivated or co-opted by the host cell for other functions.