Reverse transcriptase consists of 2 domains:
- DNA polymerase – extends nucleotide in 5′ → 3′ direction
- RNase H - an endonuclease which hydrolyses RNA when present in an RNA-DNA duplex (Sevilya et al., 2003).
Do only retroviruses, which composed of RNA and not DNA, have the RT enzyme? The simple answer is no. RT enzyme is not restricted to retroviruses (Hull R., 1999)
Retroelements, which are key genetic elements in retroviruses, carry information from one location to another within the genome through reverse transcription of an RNA intermediate and are classified into 3 groups:
- viral (retrovirus and pararetrovirus)
- bacterial (retron), and
- eukaryotic non-viral retroelements (retrotransposon and retroposon, all of which contains the RT enzyme.