Retrovirus
A retrovirus is an RNA virus that copies its genome into DNA and integrates that DNA into a host cell genome.
What a retrovirus is
A retrovirus is an enveloped virus with an RNA genome that replicates through a DNA intermediate. After entering a host cell, it uses reverse transcriptase to make DNA from its RNA. That DNA can be integrated into the host genome, creating a provirus that cellular machinery can later transcribe.
Why it is called retro
The name refers to the reverse flow of genetic information. Many cellular processes copy DNA into RNA, but retroviruses copy RNA into DNA. This does not overturn molecular biology; it adds an important pathway used by viruses and related genetic elements. The enzyme that makes this possible is reverse transcriptase.
The retroviral genome
A retroviral particle usually carries two copies of single-stranded RNA plus viral enzymes such as reverse transcriptase, integrase, and protease. The genome encodes structural proteins, enzymes, and envelope proteins. Many retroviruses also contain long terminal repeat sequences that help control transcription after integration.
From RNA to provirus
Once inside the cell, reverse transcriptase converts the viral RNA into double-stranded DNA. Integrase then inserts that DNA into a chromosome. The integrated DNA is called a provirus. From that position, host RNA polymerase can transcribe viral RNA, which can become new genomes or messenger RNAs for viral proteins.
Assembly and release
New retroviral components assemble at cellular membranes or internal compartments, depending on the virus. Viral RNA and proteins are packaged into budding particles. Protease then cuts viral polyproteins into mature functional pieces, helping the newly released virions become infectious.
HIV and other retroviruses
HIV is the best-known human retrovirus, but retroviruses are a broader group. They include lentiviruses, gammaretroviruses, deltaretroviruses, spumaviruses, and others. Some cause immune disease, some are linked to cancer, and some are studied as tools for gene delivery because integration can provide stable genetic insertion.
Endogenous retroviruses
If a retrovirus integrates into a germline cell, its proviral DNA can be inherited by future generations. Over evolutionary time, many such sequences have accumulated in animal genomes as endogenous retroviruses. Most are inactive or fragmented, but some have been co-opted for host functions, while others can influence gene regulation.
Why it matters
Retroviruses matter for medicine, evolution, biotechnology, and genome biology. They explain how RNA viruses can become stable DNA elements, why HIV drugs target reverse transcriptase, integrase, and protease, how viral sequences shaped host genomes, and why integrating vectors can be powerful but require careful safety design.