retrovirus

Any of a family of viruses (Retroviridae) that contain RNA as genetic material and are able to produce DNA copies of their RNA genes, which they incorporate into the host genome.

The retrovirus is able to transcribe RNA into DNA with the help of an enzyme encoded in its genome, known as the reverse transcriptase (since the transfer of genetic information from DNA to RNA is known as transcription, and retroviruses do the reverse of this). Retroviruses were seen as a rare and exotic exception to the rules of biology, until in the late 1980s the agents causing AIDS and some forms of leukaemia were recognized to be retroviruses.

Retroviruses are used as vectors in genetic engineering, but they cannot be used to target specific sites on the chromosome. Instead they incorporate their genes at random sites.