Provirus

A provirus is a viral genome that has integrated into the DNA of a host cell and is replicated with the host genome during cell division. In retroviruses such as HIV, the viral RNA genome is reverse-transcribed into double-stranded DNA by reverse transcriptase. The resulting DNA is integrated into the host genome by the viral integrase, creating the provirus. Once integrated, the proviral DNA is transcribed by the host RNA polymerase II to produce viral RNA transcripts, which can be translated into viral proteins and packaged into new virions. In latency, transcription is suppressed, and the provirus persists in the genome without producing infectious virions until activation signals trigger reactivation.

A related concept in bacteriophages is the prophage, the integrated phage genome in a bacterial chromosome; the term provirus is typically used for animal or human viruses.

Proviruses are a central feature of endogenous retroviruses (ERVs), which are proviral sequences that have become fixed in the germline and are inherited across generations. ERVs contribute to the host genome and, in some cases, have been co-opted for host functions, such as certain placental proteins like syncytins derived from env genes.

Clinically, proviruses pose challenges for cure strategies in persistent infections. In HIV infection, latent proviruses form a reservoir that is resistant to standard antiretroviral therapy. Strategies to purge this reservoir aim to activate latent proviruses and expose infected cells to immune clearance or cytopathic effects.

In summary, a provirus is the integrated, latent form of a viral genome within the host DNA, enabling persistence, transmission and evolution of both virus and host.