Reverse transcriptase is an enzyme used by all retroviruses that transcribes the genetic information from the virus from RNA into DNA, which can integrate into the host genome. Usually, transcription only runs from DNA to RNA, catalyzed by RNA polymerase. An example of this kind of enzyme is the reverse transcriptase from the human immunodeficiency virus type 1 (PDB 1HMV, EC 188.8.131.52).
Reverse transcriptase is commonly used in the field of research to be able to apply the Polymerase chain reaction technique to RNA. The classical PCR technique can only be applied to DNA strands, but with the help of reverse transcriptase, RNA can be transcribed into DNA making PCR analysis of RNA molecules possible. The technique is collectively called: Reverse Transcriptase Polymerase Chain Reaction (RT-PCR).